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| UK diy (uk.d-i-y) For the discussion of all topics related to diy (do-it-yourself) in the UK. All levels of experience and proficency are welcome to join in to ask questions or offer solutions. |
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#1
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5A not enough on lighting circuit?
Having a series of problems with a lighting circuit which has been fine for
2 years. Basically the total load according to my calcs is about 875w so "in theory" is okay on a 5A MCB. But, it keeps tripping whenever more than 75% lights/shower fans are running. The circuit is wired with 1mm T&E with odd bits in 1.5mm where alterations were done a couple of years back. Assuming it is just a loading issue can I put a 10A trip in or is that too much for the existing wiring? |
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#2
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5A not enough on lighting circuit?
TonyK wrote:
Having a series of problems with a lighting circuit which has been fine for 2 years. Basically the total load according to my calcs is about 875w so "in theory" is okay on a 5A MCB. But, it keeps tripping whenever more than 75% lights/shower fans are running. Does it trip when they have been running for a bit, or the instant when you switch stuff on? I think some tests on the circuit would be advised. Even a simple current measurement would tell you plenty. If you have access to one, a clamp meter placed round the live wire at the MCB in the CU would let you see the actual current drawn with no apparent load (ought to be 0) an then as you switch in each light. From there you should have a good indication as to the type of fault you are looking for, which could be a simple as a faulty MCB to a wiring or appliance problem. The circuit is wired with 1mm T&E with odd bits in 1.5mm where alterations were done a couple of years back. Assuming it is just a loading issue can I put a 10A trip in or is that too much for the existing wiring? It sounds like you have a definite problem that needs investigating and fixing. IMO uprating the protection device is *not* the way to go (even if the cable can nominally take it in ideal conditions). -- Cheers, John. /================================================== ===============\ | Internode Ltd - http://www.internode.co.uk | |-----------------------------------------------------------------| | John Rumm - john(at)internode(dot)co(dot)uk | \================================================= ================/ |
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#3
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5A not enough on lighting circuit?
"John Rumm" wrote in message ... TonyK wrote: Having a series of problems with a lighting circuit which has been fine for 2 years. Basically the total load according to my calcs is about 875w so "in theory" is okay on a 5A MCB. But, it keeps tripping whenever more than 75% lights/shower fans are running. Does it trip when they have been running for a bit, or the instant when you switch stuff on? It can run quite happily for anything up to 30 mins before it trips, it seems almost random. I think some tests on the circuit would be advised. Even a simple current measurement would tell you plenty. If you have access to one, a clamp meter placed round the live wire at the MCB in the CU would let you see the actual current drawn with no apparent load (ought to be 0) an then as you switch in each light. From there you should have a good indication as to the type of fault you are looking for, which could be a simple as a faulty MCB to a wiring or appliance problem. The circuit is wired with 1mm T&E with odd bits in 1.5mm where alterations were done a couple of years back. Assuming it is just a loading issue can I put a 10A trip in or is that too much for the existing wiring? It sounds like you have a definite problem that needs investigating and fixing. IMO uprating the protection device is *not* the way to go (even if the cable can nominally take it in ideal conditions). Second time in as many weeks I've been told I need a clamp meter. Shall add one to Mondays shopping list! Thanks |
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#4
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5A not enough on lighting circuit?
"TonyK" wrote in message ... "John Rumm" wrote in message ... TonyK wrote: Having a series of problems with a lighting circuit which has been fine for 2 years. Basically the total load according to my calcs is about 875w so "in theory" is okay on a 5A MCB. But, it keeps tripping whenever more than 75% lights/shower fans are running. Does it trip when they have been running for a bit, or the instant when you switch stuff on? It can run quite happily for anything up to 30 mins before it trips, it seems almost random. I think some tests on the circuit would be advised. Even a simple current measurement would tell you plenty. If you have access to one, a clamp meter placed round the live wire at the MCB in the CU would let you see the actual current drawn with no apparent load (ought to be 0) an then as you switch in each light. From there you should have a good indication as to the type of fault you are looking for, which could be a simple as a faulty MCB to a wiring or appliance problem. The circuit is wired with 1mm T&E with odd bits in 1.5mm where alterations were done a couple of years back. Assuming it is just a loading issue can I put a 10A trip in or is that too much for the existing wiring? It sounds like you have a definite problem that needs investigating and fixing. IMO uprating the protection device is *not* the way to go (even if the cable can nominally take it in ideal conditions). Second time in as many weeks I've been told I need a clamp meter. Shall add one to Mondays shopping list! Loose wires in a socket or to one of the fans. Could be the result of vibration and causing an intermittent load that trips the breaker |
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#5
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5A not enough on lighting circuit?
"TonyK" wrote in message ... Having a series of problems with a lighting circuit which has been fine for 2 years. Basically the total load according to my calcs is about 875w so "in theory" is okay on a 5A MCB. But, it keeps tripping whenever more than 75% lights/shower fans are running. Does it only trip when the fan motors are running/starting? |
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#6
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5A not enough on lighting circuit?
"dennis@home" wrote in message . uk... "TonyK" wrote in message ... Having a series of problems with a lighting circuit which has been fine for 2 years. Basically the total load according to my calcs is about 875w so "in theory" is okay on a 5A MCB. But, it keeps tripping whenever more than 75% lights/shower fans are running. Does it only trip when the fan motors are running/starting? Not always... there are 4x58w inline fans plus 3 x shower extractors, 6x35W 12V halogens,13x16w 2D fittings, 2x4' flourescents, 4xcombined shaver/lamps plus 4x "normal" 16w CFL lamps. This is spread over 6 rooms and ajoining hallway. You can run everything for a few minutes or a combination of rooms for half an hour, after than it gives up. It was perfectly fine for 2 years up until about 3 weeks ago. |
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#7
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5A not enough on lighting circuit?
TonyK wrote:
Does it trip when they have been running for a bit, or the instant when you switch stuff on? It can run quite happily for anything up to 30 mins before it trips, it seems almost random. That would suggest a sustained overload then. Remember that a MCB will pass current significantly above its marked value for some time. Assuming we are talking about a 6A type B MCB, then table 3.4 of BS7671 would apply. That would indicate a sustained load of some 9A to result in a trip in that time frame. Second time in as many weeks I've been told I need a clamp meter. Shall add one to Mondays shopping list! It is not essential, but it is a quicker and safer way to make these sorts of measurements. Some multimeters will measure AC current (although some that do only go up to 5A or so), but, they need to be placed in circuit to make a reading. This obviously requires disconnecting wires and finding a safe way to connect them to the meter (a good set of shielded probes with insulated croc clips - or failing that a chockie block to join the circuit wire to either the probe end, or better still a suitable shrouded banana plug). With a clamp meter you can place it round any suitable individual conductor[1] (i.e. you can't just clamp round a whole flex or cable since the current flowing back through the neutral will exactly cancel the reading you would get from the current in the live). So for example placing it round a meter tail will give you a base reading for the whole houses consumption at that moment without even needing to open the CU. Assuming this is reasonably static (i.e. no big loads switching in and out on thermostats etc) you can probably conduct useful tests with just this. [1] A useful trick with clamp meters to increase resolution of a reading is to put the clamp round several turns of the wire under test - then divide the reading by the number of turns. -- Cheers, John. /================================================== ===============\ | Internode Ltd - http://www.internode.co.uk | |-----------------------------------------------------------------| | John Rumm - john(at)internode(dot)co(dot)uk | \================================================= ================/ |
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#8
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5A not enough on lighting circuit?
On Sat, 31 Dec 2005 17:33:46 +0000, John Rumm
wrote: TonyK wrote: Does it trip when they have been running for a bit, or the instant when you switch stuff on? It can run quite happily for anything up to 30 mins before it trips, it seems almost random. That would suggest a sustained overload then. Remember that a MCB will pass current significantly above its marked value for some time. Assuming we are talking about a 6A type B MCB, then table 3.4 of BS7671 would apply. That would indicate a sustained load of some 9A to result in a trip in that time frame. Second time in as many weeks I've been told I need a clamp meter. Shall add one to Mondays shopping list! It is not essential, but it is a quicker and safer way to make these sorts of measurements. Some multimeters will measure AC current (although some that do only go up to 5A or so), but, they need to be placed in circuit to make a reading. This obviously requires disconnecting wires and finding a safe way to connect them to the meter (a good set of shielded probes with insulated croc clips - or failing that a chockie block to join the circuit wire to either the probe end, or better still a suitable shrouded banana plug). An alternative is to connect it across the circuit's switch - with the switch "off" the meter will be in circuit. -- Frank Erskine |
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#9
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5A not enough on lighting circuit?
"TonyK" wrote in message ... "dennis@home" wrote in message . uk... "TonyK" wrote in message ... Having a series of problems with a lighting circuit which has been fine for 2 years. Basically the total load according to my calcs is about 875w so "in theory" is okay on a 5A MCB. But, it keeps tripping whenever more than 75% lights/shower fans are running. Does it only trip when the fan motors are running/starting? Not always... there are 4x58w inline fans plus 3 x shower extractors, 6x35W 12V halogens,13x16w 2D fittings, 2x4' flourescents, 4xcombined shaver/lamps plus 4x "normal" 16w CFL lamps. This is spread over 6 rooms and ajoining hallway. You can run everything for a few minutes or a combination of rooms for half an hour, after than it gives up. It was perfectly fine for 2 years up until about 3 weeks ago. If you have two 5 amp MCBs on the CU then swap them over to see if the MCB is faulty. Adam |
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#10
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5A not enough on lighting circuit?
Frank Erskine wrote:
An alternative is to connect it across the circuit's switch - with the switch "off" the meter will be in circuit. Yes, good point! handy for narrowing down likely culprits if it turns out to not be the wiring itself. -- Cheers, John. /================================================== ===============\ | Internode Ltd - http://www.internode.co.uk | |-----------------------------------------------------------------| | John Rumm - john(at)internode(dot)co(dot)uk | \================================================= ================/ |
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#11
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5A not enough on lighting circuit?
TonyK wrote:
It was perfectly fine for 2 years up until about 3 weeks ago. What else has happened in the last two weeks? Any DIY going on that required holes in walls? Changed any bulbs or fittings? -- Cheers, John. /================================================== ===============\ | Internode Ltd - http://www.internode.co.uk | |-----------------------------------------------------------------| | John Rumm - john(at)internode(dot)co(dot)uk | \================================================= ================/ |
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#12
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5A not enough on lighting circuit?
"TonyK" wrote in message ... "dennis@home" wrote in message . uk... "TonyK" wrote in message ... Having a series of problems with a lighting circuit which has been fine for 2 years. Basically the total load according to my calcs is about 875w so "in theory" is okay on a 5A MCB. But, it keeps tripping whenever more than 75% lights/shower fans are running. Does it only trip when the fan motors are running/starting? Not always... there are 4x58w inline fans plus 3 x shower extractors, 6x35W 12V halogens,13x16w 2D fittings, 2x4' flourescents, 4xcombined shaver/lamps plus 4x "normal" 16w CFL lamps. This is spread over 6 rooms and ajoining hallway. Jeuss, thats some hall way / bathroom! Are you sure you dont live in a hotel?! Tim.. |
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#13
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5A not enough on lighting circuit?
"Tim (remove obvious)" wrote in message ... "TonyK" wrote in message ... "dennis@home" wrote in message . uk... "TonyK" wrote in message ... Having a series of problems with a lighting circuit which has been fine for 2 years. Basically the total load according to my calcs is about 875w so "in theory" is okay on a 5A MCB. But, it keeps tripping whenever more than 75% lights/shower fans are running. Does it only trip when the fan motors are running/starting? Not always... there are 4x58w inline fans plus 3 x shower extractors, 6x35W 12V halogens,13x16w 2D fittings, 2x4' flourescents, 4xcombined shaver/lamps plus 4x "normal" 16w CFL lamps. This is spread over 6 rooms and ajoining hallway. Jeuss, thats some hall way / bathroom! Are you sure you dont live in a hotel?! Tim.. Not far from the truth! A Youth Hostel. Bear in mind this circuit only covers about 40% of one of three floors. Now you begin to understand my problem! |
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#14
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5A not enough on lighting circuit?
"John Rumm" wrote in message ... TonyK wrote: It was perfectly fine for 2 years up until about 3 weeks ago. What else has happened in the last two weeks? Any DIY going on that required holes in walls? Changed any bulbs or fittings? AFAIK nothing has changed. :-? |
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#15
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5A not enough on lighting circuit?
In message , TonyK
writes "John Rumm" wrote in message ... TonyK wrote: It was perfectly fine for 2 years up until about 3 weeks ago. What else has happened in the last two weeks? Any DIY going on that required holes in walls? Changed any bulbs or fittings? AFAIK nothing has changed. :-? In that case upping the current rating is only going to allow whatever has gone faulty to burn / go bang better -- geoff |
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#16
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5A not enough on lighting circuit?
"raden" wrote in message ... In message , TonyK writes "John Rumm" wrote in message ... TonyK wrote: It was perfectly fine for 2 years up until about 3 weeks ago. What else has happened in the last two weeks? Any DIY going on that required holes in walls? Changed any bulbs or fittings? AFAIK nothing has changed. :-? In that case upping the current rating is only going to allow whatever has gone faulty to burn / go bang better -- geoff Yep, I'll wait until I've got a meter and can track thr problem down. |
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#17
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5A not enough on lighting circuit?
In message , TonyK
writes "dennis@home" wrote in message .uk... "TonyK" wrote in message ... Having a series of problems with a lighting circuit which has been fine for 2 years. Basically the total load according to my calcs is about 875w so "in theory" is okay on a 5A MCB. But, it keeps tripping whenever more than 75% lights/shower fans are running. Does it only trip when the fan motors are running/starting? Not always... there are 4x58w inline fans plus 3 x shower extractors, 6x35W 12V halogens,13x16w 2D fittings, 2x4' flourescents, 4xcombined shaver/lamps plus 4x "normal" 16w CFL lamps. This is spread over 6 rooms and ajoining hallway. You can run everything for a few minutes or a combination of rooms for half an hour, after than it gives up. It was perfectly fine for 2 years up until about 3 weeks ago. Something may have changed, but I think you've got a lot of low power factor loads, particularly all the 2D fittings if they're magnetic ballasts. Before these calculations get torn apart, I've made a guesstimate at the typical PF of these loads. Particularly the motor loads I'm not sure of. Anyway, Qty x Wattage / PF = VA 4 x 58 / 0.7 = 331 3 x 20 / 0.7 = 85 6 x 35 / 0.98 = 215 (transformer efficiency rather than pf) 13 x 16 / 0.7 = 297 2 x 36 / 0.7 = 103 4 x 60 / 1 = 240 (assuming 60W strip lights?) 4 x 16 /.55 = 116 Total VA = 1387, or 5.78A. So the circuit _may_ be on marginal overload anyway, although as pointed out previously a typical B breaker would take that lot pretty indefinitely. I think some actual current measurements are in order, and check any magnetic ballasts for signs of over heating (although you'd have smelt them by now if they were on their death bed and cooking). -- steve |
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#18
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5A not enough on lighting circuit?
Steven Briggs wrote:
In message , TonyK writes "dennis@home" wrote in message .uk... "TonyK" wrote in message ... Having a series of problems with a lighting circuit which has been fine for 2 years. Basically the total load according to my calcs is about 875w so "in theory" is okay on a 5A MCB. But, it keeps tripping whenever more than 75% lights/shower fans are running. Does it only trip when the fan motors are running/starting? Not always... there are 4x58w inline fans plus 3 x shower extractors, 6x35W 12V halogens,13x16w 2D fittings, 2x4' flourescents, 4xcombined shaver/lamps plus 4x "normal" 16w CFL lamps. This is spread over 6 rooms and ajoining hallway. You can run everything for a few minutes or a combination of rooms for half an hour, after than it gives up. It was perfectly fine for 2 years up until about 3 weeks ago. Something may have changed, but I think you've got a lot of low power factor loads, particularly all the 2D fittings if they're magnetic ballasts. Before these calculations get torn apart, I've made a guesstimate at the typical PF of these loads. Particularly the motor loads I'm not sure of. Anyway, Qty x Wattage / PF = VA 4 x 58 / 0.7 = 331 3 x 20 / 0.7 = 85 6 x 35 / 0.98 = 215 (transformer efficiency rather than pf) 13 x 16 / 0.7 = 297 2 x 36 / 0.7 = 103 4 x 60 / 1 = 240 (assuming 60W strip lights?) 4 x 16 /.55 = 116 Total VA = 1387, or 5.78A. So the circuit _may_ be on marginal overload anyway, although as pointed out previously a typical B breaker would take that lot pretty indefinitely. Diversity should see that lot run indefinitely. FWIW the halogen transformers and CFLs will have much worse pf than that, they will only take current at v peaks. But diversity still applies. NT |
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#19
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5A not enough on lighting circuit?
On Sat, 31 Dec 2005 21:41:32 +0000, Steven Briggs wrote:
So the circuit _may_ be on marginal overload anyway, although as pointed out previously a typical B breaker would take that lot pretty indefinitely. I think some actual current measurements are in order, and check any magnetic ballasts for signs of over heating (although you'd have smelt them by now if they were on their death bed and cooking). I agree, I'd say you are close to the limit, and possibly the circuit breaker has started to go 'sensitive'. Given the cost, I'd go for a new one of the correct rating for the wiring, before doing anything else. Its cheaper than a meter. |
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#20
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5A not enough on lighting circuit?
The Natural Philosopher wrote:
I agree, I'd say you are close to the limit, and possibly the circuit breaker has started to go 'sensitive'. Given the cost, I'd go for a new one of the correct rating for the wiring, before doing anything else. Its cheaper than a meter. I'd make it a type C as well NT |
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#21
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5A not enough on lighting circuit?
Steven Briggs wrote:
Something may have changed, but I think you've got a lot of low power factor loads, particularly all the 2D fittings if they're magnetic ballasts. Just what I was thinking ... Anyway, Qty x Wattage / PF = VA I suspect you may have overestimated some of the PFs. [Fans] 4 x 58 / 0.7 = 331 3 x 20 / 0.7 = 85 I'd guess 0.65, so 450 VA. [Halogens] 6 x 35 / 0.98 = 215 (transformer efficiency rather than pf) Efficiency would be about 95% if they're iron-cored transformers (so 220 VA), but electronic xfmrs could have a much lower PF (due to waveform distortion), so in worst case the loading might be as high as ~400 VA. [2Ds] 13 x 16 / 0.7 = 297 PF of these, unless corrected, is close to 0.5, so 410 VA, say. [Linear fluorescents] 2 x 36 / 0.7 = 103 Ditto 0.55, so 130 VA. [Shaver lights] 4 x 60 / 1 = 240 (assuming 60W strip lights?) They might be fluorescents, but let's stick to worst-case. CFLs 4 x 16 /.55 = 116 PF closer to 0.5, say 130 VA. Total VA = 1387, or 5.78A. Worst case total VA = 1760, or 7.6 A - enough to trip an old 5 A MCB (if that's what it is), but probably not a 6 A one. So the circuit _may_ be on marginal overload anyway, although as pointed out previously a typical B breaker would take that lot pretty indefinitely. I think some actual current measurements are in order, and check any magnetic ballasts for signs of over heating (although you'd have smelt them by now if they were on their death bed and cooking). The circuit is certainly capable of being overloaded and should either be spit into two, or uprated to 10 A, if the cable installation conditions allow. As has been said, test and inspect first before, uprating the breaker. And make sure that the clamp meter reads true RMS amps, otherwise the results will be fairly meaningless (even for the iron-cored loads harmonic currents will contribute significantly to the lower power factors). -- Andy |
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#22
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5A not enough on lighting circuit?
TonyK said the following on 31/12/2005 14:39:
Assuming it is just a loading issue can I put a 10A trip in or is that too much for the existing wiring? BS7671 Regulation 553-03-01 (Table 55B) applies. Overcurrent protection of lampholders (under certain circumstances) is limited to 6 Amp for SBC and SES lampholders. This is why domestic lighting circuits are always rated at 5/6A. Even if you don't have any light fittings with SBC (small bayonet) or SES (small edison screw) lamps IMHO it would still be considered bad practice to upgrade the MCB to 10A. If it turns out that you have an overloaded circuit, you should split the load onto two or more separate 5/6A MCBs. HTH |
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#23
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5A not enough on lighting circuit?
"TonyK" wrote in message ... "Tim (remove obvious)" wrote in message ... "TonyK" wrote in message ... "dennis@home" wrote in message . uk... "TonyK" wrote in message ... Having a series of problems with a lighting circuit which has been fine for 2 years. Basically the total load according to my calcs is about 875w so "in theory" is okay on a 5A MCB. But, it keeps tripping whenever more than 75% lights/shower fans are running. Does it only trip when the fan motors are running/starting? Not always... there are 4x58w inline fans plus 3 x shower extractors, 6x35W 12V halogens,13x16w 2D fittings, 2x4' flourescents, 4xcombined shaver/lamps plus 4x "normal" 16w CFL lamps. This is spread over 6 rooms and ajoining hallway. Jeuss, thats some hall way / bathroom! Are you sure you dont live in a hotel?! Tim.. Not far from the truth! A Youth Hostel. Bear in mind this circuit only covers about 40% of one of three floors. Now you begin to understand my problem! I feel that you have a duty of care to get a professional in to locate the problem. That is unless you are a competent electrician and appropriately insuredfor the work you will be carrying out. Regards Steve Dawson |
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#24
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5A not enough on lighting circuit?
In article , Stephen Dawson
writes "TonyK" wrote in message ... "Tim (remove obvious)" wrote in message ... "TonyK" wrote in message ... "dennis@home" wrote in message . uk... "TonyK" wrote in message ... Having a series of problems with a lighting circuit which has been fine for 2 years. Basically the total load according to my calcs is about 875w so "in theory" is okay on a 5A MCB. But, it keeps tripping whenever more than 75% lights/shower fans are running. Does it only trip when the fan motors are running/starting? Not always... there are 4x58w inline fans plus 3 x shower extractors, 6x35W 12V halogens,13x16w 2D fittings, 2x4' flourescents, 4xcombined shaver/lamps plus 4x "normal" 16w CFL lamps. This is spread over 6 rooms and ajoining hallway. Jeuss, thats some hall way / bathroom! Are you sure you dont live in a hotel?! Tim.. Not far from the truth! A Youth Hostel. Bear in mind this circuit only covers about 40% of one of three floors. Now you begin to understand my problem! I feel that you have a duty of care to get a professional in to locate the problem. That is unless you are a competent electrician and appropriately insuredfor the work you will be carrying out. Regards Steve Dawson Does it trip when the "extra" switch is turned on, or just with 75% running? Fans and extractors can have quite a switch on surge, as can fluorescent and halogens. I would guess that it is the surge which is the problem and Steve is right - you need an expert. -- John Alexander, Remove NOSPAM if replying by e-mail |
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#25
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5A not enough on lighting circuit?
In message , Andy Wade
writes Steven Briggs wrote: Something may have changed, but I think you've got a lot of low power factor loads, particularly all the 2D fittings if they're magnetic ballasts. Just what I was thinking ... Anyway, Qty x Wattage / PF = VA I suspect you may have overestimated some of the PFs. Yeah, I was being generous, there's a lot of detail we don't know. Efficiency would be about 95% if they're iron-cored transformers (so 220 VA), but electronic xfmrs could have a much lower PF (due to waveform distortion), so in worst case the loading might be as high as ~400 VA. FWIW, I thought electronic halogen transformers were pretty good on PF, certainly the ones I played with a while back just rectified the mains and chopped the power across a small toroidal ferrite transformer at HF. No storage capacitor to bugger up the input waveform. CFL's are crap, due to a rectifier-cap input circuit. ISTR a 20W Philips one was PF=.515, 11W was 0.575 when I measured some (Voltech power analyser). Proper electronic ballasts for linear FL's should have active power factor correction, and be pretty close to unity. Anyway, we should have added that lot up vector wise, accounted for the low PFs due to distortion rather than phase shift, etc, etc. But for a "back of the envelope" calculation, we've shown that there may be an overload problem that the original sparks toting up the bare watts figures didn't account for. -- steve |
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#26
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5A not enough on lighting circuit?
In article ,
Andy Wade writes: Just what I was thinking ... Anyway, Qty x Wattage / PF = VA I suspect you may have overestimated some of the PFs. [2Ds] 13 x 16 / 0.7 = 297 PF of these, unless corrected, is close to 0.5, so 410 VA, say. It's difficult to find specs of 2D lamps, but I suspect the tube voltage will be around 50V, which would make the uncorrected PF more like 0.25, which is 810 VA. [Linear fluorescents] 2 x 36 / 0.7 = 103 Ditto 0.55, so 130 VA. Again, tube voltage is something like 110V, which would make uncorrected PF less than 0.5, so VA could be more like 150. One possibility could be progressive failure of PF correction capacitors (if the fittings ever had them), resulting in a progressive increase in the circuit current. It's not uncommon to find PF correction capacitors going open circuit in strings of fluorescent luminares as they age (or more strictly, they short out and an internal fuse opens). -- Andrew Gabriel |
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#27
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5A not enough on lighting circuit?
"Stephen Dawson" wrote in message ... "TonyK" wrote in message ... "Tim (remove obvious)" wrote in message ... "TonyK" wrote in message ... "dennis@home" wrote in message . uk... "TonyK" wrote in message ... Having a series of problems with a lighting circuit which has been fine for 2 years. Basically the total load according to my calcs is about 875w so "in theory" is okay on a 5A MCB. But, it keeps tripping whenever more than 75% lights/shower fans are running. Does it only trip when the fan motors are running/starting? Not always... there are 4x58w inline fans plus 3 x shower extractors, 6x35W 12V halogens,13x16w 2D fittings, 2x4' flourescents, 4xcombined shaver/lamps plus 4x "normal" 16w CFL lamps. This is spread over 6 rooms and ajoining hallway. Jeuss, thats some hall way / bathroom! Are you sure you dont live in a hotel?! Tim.. Not far from the truth! A Youth Hostel. Bear in mind this circuit only covers about 40% of one of three floors. Now you begin to understand my problem! I feel that you have a duty of care to get a professional in to locate the problem. That is unless you are a competent electrician and appropriately insuredfor the work you will be carrying out. Regards Steve Dawson Yep, from the sound of the problem it doesn't look like its a simple one. I suspect the electricians that did all the work a few years back weren't "competent". It'll just have to wait until people are back at work next week. |
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#28
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5A not enough on lighting circuit?
I feel that you have a duty of care to get a professional in to locate the
problem. That is unless you are a competent electrician and appropriately insuredfor the work you will be carrying out. Does it trip when the "extra" switch is turned on, or just with 75% running? Fans and extractors can have quite a switch on surge, as can fluorescent and halogens. I would guess that it is the surge which is the problem and Steve is right - you need an expert. What am I missing: 1. the circuit is loaded up to its max rating and likely beyond 2. its behaving exactly as would be expected 3. Type C breakers are known to be better suited for lighting circuits, and would help with the switch on surge currents that are the (non-safety) problem. AFAICS there is no reason to believe anything is unsafely amiss, beyond switch on surges popping the breaker. OTOH I forget what the level of expertise of the OP is. NT |
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#29
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5A not enough on lighting circuit?
Andy Wade wrote:
Steven Briggs wrote: Something may have changed, but I think you've got a lot of low power factor loads, particularly all the 2D fittings if they're magnetic ballasts. Just what I was thinking ... Anyway, Qty x Wattage / PF = VA I suspect you may have overestimated some of the PFs. [Fans] 4 x 58 / 0.7 = 331 3 x 20 / 0.7 = 85 I'd guess 0.65, so 450 VA. [Halogens] 6 x 35 / 0.98 = 215 (transformer efficiency rather than pf) Efficiency would be about 95% if they're iron-cored transformers (so 220 VA), but electronic xfmrs could have a much lower PF (due to waveform distortion), so in worst case the loading might be as high as ~400 VA. [2Ds] 13 x 16 / 0.7 = 297 PF of these, unless corrected, is close to 0.5, so 410 VA, say. [Linear fluorescents] 2 x 36 / 0.7 = 103 Ditto 0.55, so 130 VA. [Shaver lights] 4 x 60 / 1 = 240 (assuming 60W strip lights?) They might be fluorescents, but let's stick to worst-case. CFLs 4 x 16 /.55 = 116 PF closer to 0.5, say 130 VA. Total VA = 1387, or 5.78A. Worst case total VA = 1760, or 7.6 A - enough to trip an old 5 A MCB (if that's what it is), but probably not a 6 A one. So the circuit _may_ be on marginal overload anyway, although as pointed out previously a typical B breaker would take that lot pretty indefinitely. I think some actual current measurements are in order, and check any magnetic ballasts for signs of over heating (although you'd have smelt them by now if they were on their death bed and cooking). The circuit is certainly capable of being overloaded and should either be spit into two, or uprated to 10 A, if the cable installation conditions allow. As has been said, test and inspect first before, uprating the breaker. And make sure that the clamp meter reads true RMS amps, otherwise the results will be fairly meaningless (even for the iron-cored loads harmonic currents will contribute significantly to the lower power factors). While I can happily accept the numbers, I'm not so sure I'd interpret them the same way. 7.6A of loads on a 5A circuit would not normally be a problem, due to diversity. The problem I think is less liekly the continuous ratings, more likely the surges, and the poor surge tolerance of type Bs. NT |
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#31
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5A not enough on lighting circuit?
wrote:
While I can happily accept the numbers, I'm not so sure I'd interpret them the same way. 7.6A of loads on a 5A circuit would not normally be a problem, due to diversity. The problem I think is less liekly the Depends on if they are all switched on, which is a possibility (hence why you don't use diversity for loading calce on lighting circuits). Note also however that for a 6A type B you need 8.5A to get onto the start of the thermal trip part of the curve. -- Cheers, John. /================================================== ===============\ | Internode Ltd - http://www.internode.co.uk | |-----------------------------------------------------------------| | John Rumm - john(at)internode(dot)co(dot)uk | \================================================= ================/ |
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#32
Posted to uk.d-i-y
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5A not enough on lighting circuit?
"TonyK" wrote in message news  "Stephen Dawson" wrote in message ... "TonyK" wrote in message ... "Tim (remove obvious)" wrote in message ... "TonyK" wrote in message ... "dennis@home" wrote in message . uk... "TonyK" wrote in message ... Having a series of problems with a lighting circuit which has been fine for 2 years. Basically the total load according to my calcs is about 875w so "in theory" is okay on a 5A MCB. But, it keeps tripping whenever more than 75% lights/shower fans are running. Does it only trip when the fan motors are running/starting? Not always... there are 4x58w inline fans plus 3 x shower extractors, 6x35W 12V halogens,13x16w 2D fittings, 2x4' flourescents, 4xcombined shaver/lamps plus 4x "normal" 16w CFL lamps. This is spread over 6 rooms and ajoining hallway. Jeuss, thats some hall way / bathroom! Are you sure you dont live in a hotel?! Tim.. Not far from the truth! A Youth Hostel. Bear in mind this circuit only covers about 40% of one of three floors. Now you begin to understand my problem! I feel that you have a duty of care to get a professional in to locate the problem. That is unless you are a competent electrician and appropriately insuredfor the work you will be carrying out. Regards Steve Dawson Yep, from the sound of the problem it doesn't look like its a simple one. I suspect the electricians that did all the work a few years back weren't "competent". It'll just have to wait until people are back at work next week. Where is your youth hostel?? |
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#33
Posted to uk.d-i-y
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5A not enough on lighting circuit?
Andrew Gabriel wrote:
It's difficult to find specs of 2D lamps, but I suspect the tube voltage will be around 50V, which would make the uncorrected PF more like 0.25, which is 810 VA. I'm not sure it's quite that bad. I have a Thorn Lighting data book (early 90s vintage) which gives the following data for the 16 W 2D: tube volts 97 V running current 0.2 A circuit watts 21 W total VA 48 VA circuit power factor 0.44 (uncorrected, lagging) 3rd harmonic current 17% This brings into focus the fact that the sums should be based on circuit watts (not tube watts) as the ballast losses are not negligible, especially for these small lamps. 5 watts ballast loss for a 16 W lamp is not exactly high efficiency. Anyway, 13 luminaires at 48 VA each is 624 VA total, or 2.6 amps. [Linear fluorescents] 2 x 36 / 0.7 = 103 Ditto 0.55, so 130 VA. Again, tube voltage is something like 110V, which would make uncorrected PF less than 0.5, so VA could be more like 150. Same Thorn book says 103 volts (tube), 0.43 A, 47 circuit watts. If uncorrected that would be ~100 VA each, 200 VA total (PF = 0.455). One possibility could be progressive failure of PF correction capacitors (if the fittings ever had them), The 13 2Ds are very unlikely to be corrected. The default fittings aren't, you have to select the HPF special order option (high power factor, not highpass filter!) to get a capacitor. progressive increase in the circuit current. It's not uncommon to find PF correction capacitors going open circuit in strings of fluorescent luminares as they age (or more strictly, they short out and an internal fuse opens). Certainly a possibility, although I think that's less common with modern polypropylene capacitors, compared to the old impregnated paper things. -- Andy |
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#34
Posted to uk.d-i-y
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5A not enough on lighting circuit?
Stephen Dawson wrote:
I feel that you have a duty of care to get a professional in to locate the problem. That is unless you are a competent electrician and appropriately insuredfor the work you will be carrying out. I can't see any problem with the OP at least diagnosing and locating the problem, even if he leaves fixing it to a "pro". So long as he is confident that he will not cause harm to himself (or others) in the process, there is plenty of advice available here from suitably skilled people. -- Cheers, John. /================================================== ===============\ | Internode Ltd - http://www.internode.co.uk | |-----------------------------------------------------------------| | John Rumm - john(at)internode(dot)co(dot)uk | \================================================= ================/ |
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#35
Posted to uk.d-i-y
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5A not enough on lighting circuit?
Andrew Gabriel wrote:
In article .com, writes: While I can happily accept the numbers, I'm not so sure I'd interpret them the same way. 7.6A of loads on a 5A circuit would not normally be a problem, due to diversity. There's no diversity allowed within a lighting circuit. You need to expect it can handle all lights on at the same time. IIRC its not just lighting on this circuit. The problem I think is less liekly the continuous ratings, more likely the surges, and the poor surge tolerance of type Bs. What surges are you talking about? filament bulbs, CFLs and motors all eat current surges when switched on, for a different reason in each case. NT |
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#36
Posted to uk.d-i-y
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5A not enough on lighting circuit?
John Rumm wrote:
wrote: While I can happily accept the numbers, I'm not so sure I'd interpret them the same way. 7.6A of loads on a 5A circuit would not normally be a problem, due to diversity. The problem I think is less liekly the Depends on if they are all switched on, which is a possibility (hence why you don't use diversity for loading calce on lighting circuits). Note also however that for a 6A type B you need 8.5A to get onto the start of the thermal trip part of the curve. Indeed. A 6A type C should solve the problem. The mcb would be rated in accordance with todays regs, the cable is all 7.6A rated... yes its a close one but not a danger in any way, and should solve the problem. But no way is there any room on that circuit for anything else to be added! NT |
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#37
Posted to uk.d-i-y
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5A not enough on lighting circuit?
wrote:
Indeed. A 6A type C should solve the problem. The mcb would be rated in accordance with todays regs, the cable is all 7.6A rated... yes its a close one but not a danger in any way, and should solve the problem. But no way is there any room on that circuit for anything else to be added! I would personally only be happy with that solution once I had convinced myself that there was nothing on the circuit that was actually causing the problem as a result of higher than normal power dissipation. Especially since this is a circuit that used to run ok and has not been altered recently. -- Cheers, John. /================================================== ===============\ | Internode Ltd - http://www.internode.co.uk | |-----------------------------------------------------------------| | John Rumm - john(at)internode(dot)co(dot)uk | \================================================= ================/ |
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#39
Posted to uk.d-i-y
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5A not enough on lighting circuit?
wrote in message oups.com... John Rumm wrote: wrote: While I can happily accept the numbers, I'm not so sure I'd interpret them the same way. 7.6A of loads on a 5A circuit would not normally be a problem, due to diversity. The problem I think is less liekly the Depends on if they are all switched on, which is a possibility (hence why you don't use diversity for loading calce on lighting circuits). Note also however that for a 6A type B you need 8.5A to get onto the start of the thermal trip part of the curve. Indeed. A 6A type C should solve the problem. The mcb would be rated in accordance with todays regs, the cable is all 7.6A rated... yes its a close one but not a danger in any way, and should solve the problem. But no way is there any room on that circuit for anything else to be added! NT Assuming that you check the final earth loop impedence value is in accordance with the manufacturers value. It is always nice to know that it wil attempt to trip in the event of a fault.Zs value for type B BSEN60898 is 8 ohms, for a Type C is it 4 ohm ( according to BS Devices selection from Amtech Single Cable). This may be an issue if the supply is TT or the Ze is high. Steve Dawson |
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