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Live or neutral?
I have bought a new ceiling light for my wifes latest project, an Art Deco living room ! On removing the existing fitting I found that there are only two cables both of which are coloured red!
As the new fitting has a step down transformer I assume it will be necessary to wire it correctly i.e. Live to live and neutral to neutral and somehow fit an earth (the two red cables are contained in an iron tube conduit). How do I find out which is live and which is neutral without any test equipment?? |
Live or neutral?
On Fri, 18 Jan 2008 17:50:44 +0000, Unclebill
wrote: How do I find out which is live and which is neutral without any test equipment?? I have used a couple of ways of doing this but neither are suitable for a public newsgroup since they could both be dangerous. Suggest buying a neon srewdriver. Geo |
Live or neutral?
The message
from Geo contains these words: On Fri, 18 Jan 2008 17:50:44 +0000, Unclebill wrote: How do I find out which is live and which is neutral without any test equipment?? I have used a couple of ways of doing this but neither are suitable for a public newsgroup since they could both be dangerous. Suggest buying a neon srewdriver. If so, make sure it's the old-fashioned sort, not one of those that lights up anywhere near a live supply and make sure you don't have rubber shoes and aren't standing on an insulated stepladder. However, since Maplin do perfectly serviceable multimeters in a neoprene hoster for prices which vary from £2.95 to £5, everyone can have a meter. |
Live or neutral?
"Geo" wrote in message ... On Fri, 18 Jan 2008 17:50:44 +0000, Unclebill wrote: How do I find out which is live and which is neutral without any test equipment?? I have used a couple of ways of doing this but neither are suitable for a public newsgroup since they could both be dangerous. Suggest buying a neon srewdriver. Geo I have learned to remove my neon screwdriver from my top pocket and hide it when working with real electricians. They are not excatly regarded as de rigueur. -- Graham %Profound_observation% |
Live or neutral?
On 18 Jan, 17:50, Unclebill wrote:
I have bought a new ceiling light for my wifes latest project, an Art Deco living room ! On removing the existing fitting I found that there are only two cables both of which are coloured red! As the new fitting has a step down transformer I assume it will be necessary to wire it correctly i.e. Live to live and neutral to neutral and somehow fit an earth (the two red cables are contained in an iron tube conduit). How do I find out which is live and which is neutral without any test equipment?? -- Unclebill Come on guys - not very intelligent answers. Try thinking first. The answer is that a transformer is totally insensitive to which way it is connected - it is after all just a floating coil, (or strictly a pair of coils - primary and secondary). So it doesn't matter which way it is wired. As far as the earthing is concerned, if there is no earth tag on the fitting, then it is safe to assume that any metal parts are isolated from the fitting and that a double fault would be required to make the fitting live. If on the other hand there is an expectation that the fitting should be earthed, then the OP does have a problem as it is not acceptable to consider the conduit as a an earth as it will have mechanical joints in it that may have suffered corrosion over the years The solution is I'm afraid to pull the two cables back through, pulling in new cables plus an earth cable. I would suggest that the OP gets professional advise as his original question does suggest that his knowledge of electrics is beyond such a rewiring activity. Rob |
Live or neutral?
In article ,
Unclebill wrote: I have bought a new ceiling light for my wifes latest project, an Art Deco living room ! On removing the existing fitting I found that there are only two cables both of which are coloured red! As the new fitting has a step down transformer I assume it will be necessary to wire it correctly i.e. Live to live and neutral to neutral and somehow fit an earth (the two red cables are contained in an iron tube conduit). How do I find out which is live and which is neutral without any test equipment?? I'd say you should get a book on basic theory and read it before attempting any electrical work. -- *Everyone has a photographic memory. Some don't have film * Dave Plowman London SW To e-mail, change noise into sound. |
Live or neutral?
In message , Graham.
writes "Geo" wrote in message .. . On Fri, 18 Jan 2008 17:50:44 +0000, Unclebill wrote: How do I find out which is live and which is neutral without any test equipment?? I have used a couple of ways of doing this but neither are suitable for a public newsgroup since they could both be dangerous. Suggest buying a neon srewdriver. Geo I have learned to remove my neon screwdriver from my top pocket and hide it when working with real electricians. They are not excatly regarded as de rigueur. so why not chuck it away ? -- geoff |
Live or neutral?
Unclebill wrote:
How do I find out which is live and which is neutral without any test equipment?? By buying some... -- Cheers, John. /================================================== ===============\ | Internode Ltd - http://www.internode.co.uk | |-----------------------------------------------------------------| | John Rumm - john(at)internode(dot)co(dot)uk | \================================================= ================/ |
Live or neutral?
On Fri, 18 Jan 2008 17:50:44 +0000 someone who may be Unclebill
wrote this:- As the new fitting has a step down transformer I assume it will be necessary to wire it correctly i.e. Live to live and neutral to neutral and somehow fit an earth (the two red cables are contained in an iron tube conduit). If the fitting is double insulated then there is no need for an earth. If you don't know what the symbol for double insulation is then you don't have the necessary skills to do the work. -- David Hansen, Edinburgh I will *always* explain revoked encryption keys, unless RIP prevents me http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54 |
Live or neutral?
On Fri, 18 Jan 2008 14:02:20 -0800 (PST) someone who may be
robgraham wrote this:- If on the other hand there is an expectation that the fitting should be earthed, then the OP does have a problem as it is not acceptable to consider the conduit as a an earth as it will have mechanical joints in it that may have suffered corrosion over the years The solution is I'm afraid to pull the two cables back through, pulling in new cables plus an earth cable. Pull them back to where? All the way to the consumer unit? That might be difficult in many conduit systems, as there is unlikely to be a wire going all the way even if there is space in the conduit. An alternative is to measure the impedance of the conduit. Despite the statements of some, conduit can make a perfectly good protective conductor provided it was installed and maintained properly. A short flying lead connected to a bolt tapped into the box is then all that is needed. However, it is vital to measure the PSC at the box and check that a small copper conductor can cope with this. It may be necessary to use a larger size than would be standard in a T&E cable. -- David Hansen, Edinburgh I will *always* explain revoked encryption keys, unless RIP prevents me http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54 |
Live or neutral?
In message , David Hansen
writes However, it is vital to measure the PSC at the box and check that a small copper conductor can cope with this. It may be necessary to use a larger size than would be standard in a T&E cable. I know what T&E is but PSC? -- Si |
Live or neutral?
On Sat, 19 Jan 2008 09:14:51 +0000 someone who may be Si
$3o&m wrote this:- I know what T&E is but PSC? Prospective short-circuit current. The hundreds or thousands of amps that will flow at that point if there is a short-circuit. It should only flow for a short period before the protective device operates, but the wiring has to be able to take this current while it flows if there is not to be further damage to the wiring. -- David Hansen, Edinburgh I will *always* explain revoked encryption keys, unless RIP prevents me http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54 |
Live or neutral?
In message , David Hansen
writes On Sat, 19 Jan 2008 09:14:51 +0000 someone who may be Si $3o&m wrote this:- I know what T&E is but PSC? Prospective short-circuit current. The hundreds or thousands of amps that will flow at that point if there is a short-circuit. It should only flow for a short period before the protective device operates, but the wiring has to be able to take this current while it flows if there is not to be further damage to the wiring. ta -- Si |
Live or neutral?
"John Rumm" wrote in message ... Unclebill wrote: How do I find out which is live and which is neutral without any test equipment?? By buying some... Impovise, wet your finger and touch the wires in turn. You will soon find the live cable. It will save you a few quid. Adam |
Live or neutral?
Si wrote:
In message , David Hansen writes On Sat, 19 Jan 2008 09:14:51 +0000 someone who may be Si $3o&m wrote this:- I know what T&E is but PSC? Prospective short-circuit current. The hundreds or thousands of amps that will flow at that point if there is a short-circuit. It should only flow for a short period before the protective device operates, but the wiring has to be able to take this current while it flows if there is not to be further damage to the wiring. ta It would actually be more appropriate to measure the Earth Fault Loop impedance since it is the integrity of the earth that is in question. -- Cheers, John. /================================================== ===============\ | Internode Ltd - http://www.internode.co.uk | |-----------------------------------------------------------------| | John Rumm - john(at)internode(dot)co(dot)uk | \================================================= ================/ |
Live or neutral?
John Rumm wrote:
It would actually be more appropriate to measure the Earth Fault Loop impedance since it is the integrity of the earth that is in question. Quite so. Short circuit compliance can be taken as read if the rating of the cable exceeds that of the fuse or circuit breaker protecting it. -- Andy |
Live or neutral?
On Sat, 19 Jan 2008 16:01:24 +0000 someone who may be John Rumm
wrote this:- It would actually be more appropriate to measure the Earth Fault Loop impedance since it is the integrity of the earth that is in question. Quite right. My mistake. -- David Hansen, Edinburgh I will *always* explain revoked encryption keys, unless RIP prevents me http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54 |
Live or neutral?
On Sun, 27 Jan 2008 21:30:06 +0000, Unclebill wrote:
I bought a multimeter, checked that the conduit really is a good earth You can't do that properly with a multimeter. It doesn't take many ohms to stop high enough fault currents from flowing and thus any overload/fault protection from operating within the time it should. -- Cheers Dave. pam is missing e-mail |
Live or neutral?
In article ,
Unclebill wrote: I bought a multimeter, checked that the conduit really is a good earth and found out which cable was which. How did you do this with a multi-meter? -- *Experience is something you don't get until just after you need it * Dave Plowman London SW To e-mail, change noise into sound. |
Quote:
"Not much can be done without a meter. For a simple voltage test like this, one of the 10 quid argos digital multimeters would be sufficient. You could also use a test lamp, but this would not give an accurate result of whether or not the steel conduit was properly earthed" |
Quote:
"it is likely that the metal conduit is being used as the earth, this is standard practice with metal conduit or trunking Assuming you have a test meter, and assuming that one of the reds is an unsleeved neutral, then measring between both reds will show 230V, measuring between one of the reds and the conduit will show 230V, this is your phase conductor (and also proves the conduit is earth), then measure the other conductor to conduit should show 0V, this is your neutral and should be sleeved black. Obviously working safely, etc etc |
Live or neutral?
On Mon, 28 Jan 2008 23:07:41 UTC, Unclebill
wrote: Dave Plowman (News);1815186 Wrote: In article , Unclebill wrote:- I bought a multimeter, checked that the conduit really is a good earth and found out which cable was which.- How did you do this with a multi-meter? I followed the advice received from another well known forum :- Which forum would that be? "Not much can be done without a meter. For a simple voltage test like this, one of the 10 quid argos digital multimeters would be sufficient. This isn't a voltage test, it's a resistance test. And you are measuring very low resistances - which a multimeter like that won't do. -- The information contained in this post is copyright the poster, and specifically may not be published in, or used by http://www.diybanter.com |
Live or neutral?
In article ,
Unclebill wrote: Dave Plowman (News);1815186 Wrote: In article , Unclebill wrote:- I bought a multimeter, checked that the conduit really is a good earth and found out which cable was which.- How did you do this with a multi-meter? I followed the advice received from another well known forum :- "Not much can be done without a meter. For a simple voltage test like this, one of the 10 quid argos digital multimeters would be sufficient. Then it's poor advice for checking an earth. Digital multimeters draw very little current and a poor earth with a high resistance - and this is exactly what can happen with conduit - will show up as 'normal' with one. You could also use a test lamp, but this would not give an accurate result of whether or not the steel conduit was properly earthed" In actual fact the reverse. A test lamp will draw some current and is better than a simple volt meter. But the correct tester will draw a very high current for an instant thus checking the earth is doing its job correctly - ie capable of drawing enough current in event of a fault to trip the circuit protector within the design time. -- *What am I? Flypaper for freaks!? Dave Plowman London SW To e-mail, change noise into sound. |
Live or neutral?
In an earlier contribution to this discussion,
Unclebill wrote: Dave Plowman (News);1815186 Wrote: In article , Unclebill wrote:- I bought a multimeter, checked that the conduit really is a good earth and found out which cable was which.- How did you do this with a multi-meter? I followed the advice received from another well known forum :- That says it all! -- Cheers, Roger ______ Email address maintained for newsgroup use only, and not regularly monitored.. Messages sent to it may not be read for several weeks. PLEASE REPLY TO NEWSGROUP! |
Live or neutral?
Dave Plowman (News) wrote:
better than a simple volt meter. But the correct tester will draw a very high current for an instant thus checking the earth is doing its job correctly - ie capable of drawing enough current in event of a fault to trip the circuit protector within the design time. Which raises an interesting point; many modern loop testers have a "no trip" test facility that enables measurements to be made without tripping any RCD on the circuit. With the increasing use of RCDs this will become the typical way a test like this is done. How many of them I wonder are still able to do a high current test without tripping the RCD? -- Cheers, John. /================================================== ===============\ | Internode Ltd - http://www.internode.co.uk | |-----------------------------------------------------------------| | John Rumm - john(at)internode(dot)co(dot)uk | \================================================= ================/ |
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