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#1
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Question about sub-main sizing
My TNC-S supply enters in the attached garage, where the tails are split
to a CU (in the garage, feeding: the kitchen, cooker, utility and a few other bits) and a 60A switched fuse which feeds a 16mm2 sub-main. The sub-main is about 20m long and connects to an ancient fuse board that supplies the house radial and ring outlets. A second fuse board in the same location is connected to one of the MCBs in the CU via a 2.5mm2 cable and supplies power to most of the house lights. My plan *has* been to fit a new CU close to the garage and extend all the cables back to it, but that requires a lot of disruption. I'm now wondering whether I should simply replace the two wylex boards with a single new (RCBO) CU in their present position and feed it from the sub-main. From some quick checks the existing 16mm2 will be OK at 20m for volts drop if I protect it with a 50A MCB. However, from a quick look (more poking around required) the only earth connection seems to be the CPC in the 16mm2 T&E so that will need improving and the disruption involved won't be much less than extending all the circuits, although it will be less work. What do the relevant panel experts think? |
#3
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Question about sub-main sizing
On 07/02/2019 17:57, John Rumm wrote:
On 07/02/2019 14:24, wrote: My TNC-S supply enters in the attached garage, where the tails are split to a CU (in the garage, feeding: the kitchen, cooker, utility and a few other bits) and a 60A switched fuse which feeds a 16mm2 sub-main. The sub-main is about 20m long and connects to an ancient fuse board that supplies the house radial and ring outlets. A second fuse board in the same location is connected to one of the MCBs in the CU via a 2.5mm2 cable and supplies power to most of the house lights. My plan *has* been to fit a new CU close to the garage and extend all the cables back to it, but that requires a lot of disruption. I'm now wondering whether I should simply replace the two wylex boards with a single new (RCBO) CU in their present position and feed it from the sub-main. Yup, that sounds like a less disruptive option. Â*From some quick checks the existing 16mm2 will be OK at 20m for volts drop if I protect it with a 50A MCB. However, from a quick look (more poking around required) the only earth connection seems to be the CPC in the 16mm2 T&E so that will need improving and the disruption involved won't be much less than extending all the circuits, although it will be less work. Since its a PME head end, the sub main will need to extend the main equipotential zone to the new CU. So its earth will not only need to meet the requirements of being a functional earth, but also a main bonding conductor between supply and CU. That means you need 10mm^2 of copper or equal or better amount of copper equivalent via some other means. What do the relevant panel experts think? You could either run a separate main bonding conductor (10mm^2 green/yellow single), or upgrade the T&E to say a 3 core SWA, and parallel the armour with one of the cores. .... snipped Thanks John, that was what I thought. The existing 16mm2 T&E runs between joists (mostly just resting on the ceiling, rather than being clipped) from the garage to the fuse boards so it's going to be a (necessary) pain to lift carpets and boards to run the green/yellow, but it would be more of a pain to replace it with SWA - why would I consider doing that? I haven't been able to find the rules for sub-main protection. Is it permissible to run it from a 50A DP MCB in the garage CU, or does have to be from a separate DP fused/switch from a Henley block? |
#4
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Question about sub-main sizing
I've not got tables to hand but check your earth loop impedance against disconnection times for the 40A mcb
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#5
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Question about sub-main sizing
On 07/02/2019 18:50, Cynic wrote:
I've not got tables to hand but check your earth loop impedance against disconnection times for the 40A mcb The sub-main earth loop impedance (20m of 10mm2 and 20m of 16mm2) should be about 60mOhm (37mOhm + 23mOhm) so about 0.4 ohms total (TN-C-S) - about 600A fault current. A type C MCB needs 10x rated current, so 500A for a 50A MCB. Unless I've boobed it should be OK. |
#6
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Question about sub-main sizing
On 07/02/2019 18:38, wrote:
On 07/02/2019 17:57, John Rumm wrote: On 07/02/2019 14:24, wrote: My TNC-S supply enters in the attached garage, where the tails are split to a CU (in the garage, feeding: the kitchen, cooker, utility and a few other bits) and a 60A switched fuse which feeds a 16mm2 sub-main. The sub-main is about 20m long and connects to an ancient fuse board that supplies the house radial and ring outlets. A second fuse board in the same location is connected to one of the MCBs in the CU via a 2.5mm2 cable and supplies power to most of the house lights. My plan *has* been to fit a new CU close to the garage and extend all the cables back to it, but that requires a lot of disruption. I'm now wondering whether I should simply replace the two wylex boards with a single new (RCBO) CU in their present position and feed it from the sub-main. Yup, that sounds like a less disruptive option. Â*From some quick checks the existing 16mm2 will be OK at 20m for volts drop if I protect it with a 50A MCB. However, from a quick look (more poking around required) the only earth connection seems to be the CPC in the 16mm2 T&E so that will need improving and the disruption involved won't be much less than extending all the circuits, although it will be less work. Since its a PME head end, the sub main will need to extend the main equipotential zone to the new CU. So its earth will not only need to meet the requirements of being a functional earth, but also a main bonding conductor between supply and CU. That means you need 10mm^2 of copper or equal or better amount of copper equivalent via some other means. What do the relevant panel experts think? You could either run a separate main bonding conductor (10mm^2 green/yellow single), or upgrade the T&E to say a 3 core SWA, and parallel the armour with one of the cores. ... snipped Thanks John, that was what I thought. The existing 16mm2 T&E runs between joists (mostly just resting on the ceiling, rather than being clipped) from the garage to the fuse boards so it's going to be a (necessary) pain to lift carpets and boards to run the green/yellow, but it would be more of a pain to replace it with SWA - why would I consider doing that? You could use the T&E as a draw wire to pull in the single SWA that would give you both power, earthing, and EQ bonding. I haven't been able to find the rules for sub-main protection. Is it permissible to run it from a 50A DP MCB in the garage CU, or does have to be from a separate DP fused/switch from a Henley block? No you can run from a MCB without any problem. Its commonly done. -- Cheers, John. /================================================== ===============\ | Internode Ltd - http://www.internode.co.uk | |-----------------------------------------------------------------| | John Rumm - john(at)internode(dot)co(dot)uk | \================================================= ================/ |
#7
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Question about sub-main sizing
On 07/02/2019 23:01, John Rumm wrote:
On 07/02/2019 18:38, wrote: On 07/02/2019 17:57, John Rumm wrote: On 07/02/2019 14:24, wrote: My TNC-S supply enters in the attached garage, where the tails are split to a CU (in the garage, feeding: the kitchen, cooker, utility and a few other bits) and a 60A switched fuse which feeds a 16mm2 sub-main. The sub-main is about 20m long and connects to an ancient fuse board that supplies the house radial and ring outlets. A second fuse board in the same location is connected to one of the MCBs in the CU via a 2.5mm2 cable and supplies power to most of the house lights. My plan *has* been to fit a new CU close to the garage and extend all the cables back to it, but that requires a lot of disruption. I'm now wondering whether I should simply replace the two wylex boards with a single new (RCBO) CU in their present position and feed it from the sub-main. Yup, that sounds like a less disruptive option. Â*From some quick checks the existing 16mm2 will be OK at 20m for volts drop if I protect it with a 50A MCB. However, from a quick look (more poking around required) the only earth connection seems to be the CPC in the 16mm2 T&E so that will need improving and the disruption involved won't be much less than extending all the circuits, although it will be less work. Since its a PME head end, the sub main will need to extend the main equipotential zone to the new CU. So its earth will not only need to meet the requirements of being a functional earth, but also a main bonding conductor between supply and CU. That means you need 10mm^2 of copper or equal or better amount of copper equivalent via some other means. What do the relevant panel experts think? You could either run a separate main bonding conductor (10mm^2 green/yellow single), or upgrade the T&E to say a 3 core SWA, and parallel the armour with one of the cores. ... snipped Thanks John, that was what I thought. The existing 16mm2 T&E runs between joists (mostly just resting on the ceiling, rather than being clipped) from the garage to the fuse boards so it's going to be a (necessary) pain to lift carpets and boards to run the green/yellow, but it would be more of a pain to replace it with SWA - why would I consider doing that? You could use the T&E as a draw wire to pull in the single SWA that would give you both power, earthing, and EQ bonding. Yes, but it's not going to be simple to draw SWA through joist cut-outs. Why should I consider replacing the existing T&E with SWA rather than simply adding a 10mm2 or 16mm2 green/yellow? I haven't been able to find the rules for sub-main protection. Is it permissible to run it from a 50A DP MCB in the garage CU, or does have to be from a separate DP fused/switch from a Henley block? No you can run from a MCB without any problem. Its commonly done. Is SP permissible, or does it need to be DP? |
#8
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Question about sub-main sizing
On 07/02/2019 23:36, wrote:
On 07/02/2019 23:01, John Rumm wrote: On 07/02/2019 18:38, wrote: On 07/02/2019 17:57, John Rumm wrote: On 07/02/2019 14:24, wrote: My TNC-S supply enters in the attached garage, where the tails are split to a CU (in the garage, feeding: the kitchen, cooker, utility and a few other bits) and a 60A switched fuse which feeds a 16mm2 sub-main. The sub-main is about 20m long and connects to an ancient fuse board that supplies the house radial and ring outlets. A second fuse board in the same location is connected to one of the MCBs in the CU via a 2.5mm2 cable and supplies power to most of the house lights. My plan *has* been to fit a new CU close to the garage and extend all the cables back to it, but that requires a lot of disruption. I'm now wondering whether I should simply replace the two wylex boards with a single new (RCBO) CU in their present position and feed it from the sub-main. Yup, that sounds like a less disruptive option. Â*From some quick checks the existing 16mm2 will be OK at 20m for volts drop if I protect it with a 50A MCB. However, from a quick look (more poking around required) the only earth connection seems to be the CPC in the 16mm2 T&E so that will need improving and the disruption involved won't be much less than extending all the circuits, although it will be less work. Since its a PME head end, the sub main will need to extend the main equipotential zone to the new CU. So its earth will not only need to meet the requirements of being a functional earth, but also a main bonding conductor between supply and CU. That means you need 10mm^2 of copper or equal or better amount of copper equivalent via some other means. What do the relevant panel experts think? You could either run a separate main bonding conductor (10mm^2 green/yellow single), or upgrade the T&E to say a 3 core SWA, and parallel the armour with one of the cores. ... snipped Thanks John, that was what I thought. The existing 16mm2 T&E runs between joists (mostly just resting on the ceiling, rather than being clipped) from the garage to the fuse boards so it's going to be a (necessary) pain to lift carpets and boards to run the green/yellow, but it would be more of a pain to replace it with SWA - why would I consider doing that? You could use the T&E as a draw wire to pull in the single SWA that would give you both power, earthing, and EQ bonding. Yes, but it's not going to be simple to draw SWA through joist cut-outs. Why should I consider replacing the existing T&E with SWA rather than simply adding a 10mm2 or 16mm2 green/yellow? You can do whichever is easiest and meets the required spec. Sometimes adding a wire can be more difficult that pulling in a new one. However much will depend on the detail. I haven't been able to find the rules for sub-main protection. Is it permissible to run it from a 50A DP MCB in the garage CU, or does have to be from a separate DP fused/switch from a Henley block? No you can run from a MCB without any problem. Its commonly done. Is SP permissible, or does it need to be DP? MCBs are typically SP, but you will have DP switching at the destination CU, and also at the source CU via the main switches, so the switching on the circuit protection does not matter as such so long as it can break the circuit in the even of a fault. -- Cheers, John. /================================================== ===============\ | Internode Ltd - http://www.internode.co.uk | |-----------------------------------------------------------------| | John Rumm - john(at)internode(dot)co(dot)uk | \================================================= ================/ |
#9
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Question about sub-main sizing
In article ,
John Rumm writes: On 07/02/2019 18:38, wrote: I haven't been able to find the rules for sub-main protection. Is it permissible to run it from a 50A DP MCB in the garage CU, or does have to be from a separate DP fused/switch from a Henley block? No you can run from a MCB without any problem. Its commonly done. One problem with using an MCB is you may get little if any discrimination between that, and the downstream consumer unit MCBs in the event of a fault. So if something shorts out on a final circuit, you are quite likely to find the upstream 40/50A MCB trips, and you lose power on all the final circuits on that submain. A BS1361 HRC cartridge fuse used to be a better bet, but they have vanished (spare fuses still available, but new fuse holders are not). -- Andrew Gabriel [email address is not usable -- followup in the newsgroup] |
#10
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Question about sub-main sizing
On 08/02/2019 12:26, Andrew Gabriel wrote:
In article , John Rumm writes: On 07/02/2019 18:38, wrote: I haven't been able to find the rules for sub-main protection. Is it permissible to run it from a 50A DP MCB in the garage CU, or does have to be from a separate DP fused/switch from a Henley block? No you can run from a MCB without any problem. Its commonly done. One problem with using an MCB is you may get little if any discrimination between that, and the downstream consumer unit MCBs in the event of a fault. So if something shorts out on a final circuit, you are quite likely to find the upstream 40/50A MCB trips, and you lose power on all the final circuits on that submain. A BS1361 HRC cartridge fuse used to be a better bet, but they have vanished (spare fuses still available, but new fuse holders are not). I was planning to use a 50A type C MCB to protect the sub-main and 16A type B RCBOs in the new CU - this should give discrimination. The reason for using 16A, rather than 32A, is that I have several radials and one ring with spurs. All the high current loads are fed from the other CU, in the garage. |
#11
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Question about sub-main sizing
On 08/02/2019 12:26, Andrew Gabriel wrote:
In article , John Rumm writes: On 07/02/2019 18:38, wrote: I haven't been able to find the rules for sub-main protection. Is it permissible to run it from a 50A DP MCB in the garage CU, or does have to be from a separate DP fused/switch from a Henley block? No you can run from a MCB without any problem. Its commonly done. One problem with using an MCB is you may get little if any discrimination between that, and the downstream consumer unit MCBs in the event of a fault. So if something shorts out on a final circuit, you are quite likely to find the upstream 40/50A MCB trips, and you lose power on all the final circuits on that submain. A BS1361 HRC cartridge fuse used to be a better bet, but they have vanished (spare fuses still available, but new fuse holders are not). Yup, I have noticed that CU MCB based fuse carries are much harder to find these days. If you can size your sub main MCB a couple of ratings higher than the highest downstream one, or, fit a type C at the sub main head end, you might be able to mitigate the discrimination problems. Having said that there are no guarantees, ISTR Adam mentioning a case where an appliance fault took out the main incomer fuse, leaving its plug fuse un-blown and the circuit MCB un-tripped! -- Cheers, John. /================================================== ===============\ | Internode Ltd - http://www.internode.co.uk | |-----------------------------------------------------------------| | John Rumm - john(at)internode(dot)co(dot)uk | \================================================= ================/ |
#12
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Question about sub-main sizing
On 07/02/2019 19:17, wrote:
On 07/02/2019 18:50, Cynic wrote: I've not got tables to hand but check your earth loop impedance against disconnection times for the 40A mcb The sub-main earth loop impedance (20m of 10mm2 and 20m of 16mm2) should be about 60mOhm (37mOhm + 23mOhm) so about 0.4 ohms total (TN-C-S) - about 600A fault current. A type C MCB needs 10x rated current, so 500A for a 50A MCB. Unless I've boobed it should be OK. You might have boobed it - twice, if I am not mistaken! 1. You are using 240V not 230V for your fault current. (Max Ze for a 50A C type is 0.37ohm and remember that is when the cables are at 40 deg) 2. Your resistance calculations should be 16mm earth and 16mm live (unless you wish to chop out the 6mm cpc of the 16mm T&E and not bother using it) Either way you are over the 0.37 ohms allowed. It might be better to swap the head end with some thing like this https://www.tlc-direct.co.uk/Products/CGMSF100.html -- Adam |
#13
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Question about sub-main sizing
On 08/02/2019 17:00, John Rumm wrote:
Having said that there are no guarantees, ISTR Adam mentioning a case where an appliance fault took out the main incomer fuse, leaving its plug fuse un-blown and the circuit MCB un-tripped! You are close John. Two cases where this sort of thing has happened. 1. 1970s bungalow. Tried to slacken off the cooker switch from the back box and the live cable fell out the terminal and shorted to earth. This took out the house fuse but left the 30A fuse wire intact. I'll put that down to an old fuse. 2. Flats with a 16mm T&E submain supply to each flat. A fault[1] on the lighting circuit took out the 6A lighting MCB and the 63A head end MCB. In this case there was no 10mm extra earth cable from the head end to the flat as no supplementary bonding was needed (no gas and a plastic water supply) and it would be very similar to the OPs set up. The 80A BS1361 fuse in the suppliers cut out was OK. [1] It was LE short in a new light fitting the tenant had fitted. -- Adam |
#14
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Question about sub-main sizing
On 07/02/2019 19:17, wrote:
On 07/02/2019 18:50, Cynic wrote: I've not got tables to hand but check your earth loop impedance against disconnection times for the 40A mcb The sub-main earth loop impedance (20m of 10mm2 and 20m of 16mm2) should be about 60mOhm (37mOhm + 23mOhm) so about 0.4 ohms total (TN-C-S) - about 600A fault current. A type C MCB needs 10x rated current, so 500A for a 50A MCB. Unless I've boobed it should be OK. I think I must be missing something here... where does the 20m of 10mm^2 come into this? Looking at just the submain as it currently stands: 16mm^2 T&E has a round trip resistance live + CPC of 4.23 mOhms/meter [1], so that is a contribution of 85 mOhms. If we are going with the standard estimate of 0.35 Ohms for the supply impedance (in the absence of a measurement), that gives a total Zs of 0.435 Ohms. So just inside the limit for a 50A Type C using the new cMin adjusted max ELI factors[2]. So a prospective fault current of 230 / 0.435 = 525A, adequate to trip in the instant part of the curve. Now if you increase the CPC size to 16mm^2 with the addition of a 10mm^2 single, then the situation improves further? [1] http://wiki.diyfaq.org.uk/index.php/...sistance_table [2] http://wiki.diyfaq.org.uk/index.php/...2C_Cmin_factor -- Cheers, John. /================================================== ===============\ | Internode Ltd - http://www.internode.co.uk | |-----------------------------------------------------------------| | John Rumm - john(at)internode(dot)co(dot)uk | \================================================= ================/ |
#15
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Question about sub-main sizing
On 10/02/2019 21:26, John Rumm wrote:
On 07/02/2019 19:17, wrote: On 07/02/2019 18:50, Cynic wrote: I've not got tables to hand but check your earth loop impedance against disconnection times for the 40A mcb The sub-main earth loop impedance (20m of 10mm2 and 20m of 16mm2) should be about 60mOhm (37mOhm + 23mOhm) so about 0.4 ohms total (TN-C-S) - about 600A fault current. A type C MCB needs 10x rated current, so 500A for a 50A MCB. Unless I've boobed it should be OK. I think I must be missing something here... where does the 20m of 10mm^2 come into this? Looking at just the submain as it currently stands: 16mm^2 T&E has a round trip resistance live + CPC of 4.23 mOhms/meter [1], so that is a contribution of 85 mOhms. If we are going with the standard estimate of 0.35 Ohms for the supply impedance (in the absence of a measurement), that gives a total Zs of 0.435 Ohms. So just inside the limit for a 50A Type C using the new cMin adjusted max ELI factors[2]. So a prospective fault current of 230 / 0.435 = 525A, adequate to trip in the instant part of the curve. Now if you increase the CPC size to 16mm^2 with the addition of a 10mm^2 single, then the situation improves further? Of course the second boobie makes things better:-) And I got the resistance of 16mm plus 16mm wrong in my calcs. -- Adam |
#16
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Question about sub-main sizing
On 10/02/2019 20:30, ARW wrote:
On 07/02/2019 19:17, wrote: On 07/02/2019 18:50, Cynic wrote: I've not got tables to hand but check your earth loop impedance against disconnection times for the 40A mcb The sub-main earth loop impedance (20m of 10mm2 and 20m of 16mm2) should be about 60mOhm (37mOhm + 23mOhm) so about 0.4 ohms total (TN-C-S) - about 600A fault current. A type C MCB needs 10x rated current, so 500A for a 50A MCB. Unless I've boobed it should be OK. You might have boobed itÂ* - twice, if I am not mistaken! 1. You are using 240V not 230V for your fault current. (Max Ze for a 50A C type is 0.37ohm and remember that is when the cables are at 40 deg) 2. Your resistance calculations should be 16mm earth and 16mm live (unless you wish to chop out the 6mm cpc of the 16mm T&E and not bother using it) Either way you are over the 0.37 ohms allowed. It might be better to swap the head end with some thing like this https://www.tlc-direct.co.uk/Products/CGMSF100.html Yes, it's always better when boobs appear as a pair ;-) I'd done the quick check at 230 but old habits (my fingers initially typed old hobbits) die hard so 240 reappeared when I did the proper check. When I decided to add the 10mm2 cable the brain forgot about the existing CPC. I can't think of an excuse for that :-( As you spotted, there was a third boob in your calcs ... brings back memories of a character from HHG2TTG ;-) |
#17
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Question about sub-main sizing
On 10/02/2019 21:26, John Rumm wrote:
On 07/02/2019 19:17, wrote: On 07/02/2019 18:50, Cynic wrote: I've not got tables to hand but check your earth loop impedance against disconnection times for the 40A mcb The sub-main earth loop impedance (20m of 10mm2 and 20m of 16mm2) should be about 60mOhm (37mOhm + 23mOhm) so about 0.4 ohms total (TN-C-S) - about 600A fault current. A type C MCB needs 10x rated current, so 500A for a 50A MCB. Unless I've boobed it should be OK. I think I must be missing something here... where does the 20m of 10mm^2 come into this? Sadly, it was me that was missing something - I'd forgotten about the extg CPC being in parallel with the new single. I must be getting old. Looking at just the submain as it currently stands: 16mm^2 T&E has a round trip resistance live + CPC of 4.23 mOhms/meter [1], so that is a contribution of 85 mOhms. If we are going with the standard estimate of 0.35 Ohms for the supply impedance (in the absence of a measurement), that gives a total Zs of 0.435 Ohms. So just inside the limit for a 50A Type C using the new cMin adjusted max ELI factors[2]. So a prospective fault current of 230 / 0.435 = 525A, adequate to trip in the instant part of the curve. Now if you increase the CPC size to 16mm^2 with the addition of a 10mm^2 single, then the situation improves further? [1] http://wiki.diyfaq.org.uk/index.php/...sistance_table [2] http://wiki.diyfaq.org.uk/index.php/...2C_Cmin_factor |
#18
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Question about sub-main sizing
On 11/02/2019 11:15, wrote:
On 10/02/2019 20:30, ARW wrote: You might have boobed itÂ* - twice, if I am not mistaken! 1. You are using 240V not 230V for your fault current. (Max Ze for a 50A C type is 0.37ohm and remember that is when the cables are at 40 deg) 2. Your resistance calculations should be 16mm earth and 16mm live (unless you wish to chop out the 6mm cpc of the 16mm T&E and not bother using it) Either way you are over the 0.37 ohms allowed. It might be better to swap the head end with some thing like this https://www.tlc-direct.co.uk/Products/CGMSF100.html Yes, it's always better when boobs appear as a pair ;-) I'd done the quick check at 230 but old habits (my fingers initially typed old hobbits) die hard so 240 reappeared when I did the proper check. When I decided to add the 10mm2 cable the brain forgot about the existing CPC. I can't think of an excuse for that :-( As you spotted, there was a third boob in your calcs ... brings back memories of a character from HHG2TTG ;-) I am glad someone like the bit of humour I try to put into some of my posts. The actual fused isolator I was looking for (should you go that route) is the Scolmore DB750. But I am sure the one I linked to is the same thing. Scolmore one here https://www.rselectricalsupplies.co....ched-db750_813 There is a shroud showing on the first link that allows T&E to enter properly. -- Adam |
#19
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Question about sub-main sizing
On 08/02/2019 16:25, wrote:
On 08/02/2019 12:26, Andrew Gabriel wrote: In article , Â*Â*Â*Â*John Rumm writes: On 07/02/2019 18:38, wrote: I haven't been able to find the rules for sub-main protection. Is it permissible to run it from a 50A DP MCB in the garage CU, or does have to be from a separate DP fused/switch from a Henley block? No you can run from a MCB without any problem. Its commonly done. One problem with using an MCB is you may get little if any discrimination between that, and the downstream consumer unit MCBs in the event of a fault. So if something shorts out on a final circuit, you are quite likely to find the upstream 40/50A MCB trips, and you lose power on all the final circuits on that submain. A BS1361 HRC cartridge fuse used to be a better bet, but they have vanished (spare fuses still available, but new fuse holders are not). I was planning to use a 50A type C MCB to protect the sub-main and 16A type B RCBOs in the new CU - this should give discrimination. The reason for using 16A, rather than 32A, is that I have several radials and one ring with spurs. All the high current loads are fed from the other CU, in the garage. That was the second point I meant to ask you about (I was tired yesterday as I had had a weekend off work). That's more about diversity than discrimination. http://wiki.diyfaq.org.uk/index.php/Diversity is worth a read if you have not already seen it. -- Adam |
#20
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Question about sub-main sizing
On Monday, 11 February 2019 19:12:16 UTC, ARW wrote:
On 11/02/2019 11:15, wrote: On 10/02/2019 20:30, ARW wrote: Yes, it's always better when boobs appear as a pair ;-) I'd done the quick check at 230 but old habits (my fingers initially typed old hobbits) die hard so 240 reappeared when I did the proper check. When I decided to add the 10mm2 cable the brain forgot about the existing CPC. I can't think of an excuse for that :-( As you spotted, there was a third boob in your calcs ... brings back memories of a character from HHG2TTG ;-) If there are 3 boobs something is very wrong. NT |
#21
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Question about sub-main sizing
On 11/02/2019 19:12, ARW wrote:
On 11/02/2019 11:15, wrote: On 10/02/2019 20:30, ARW wrote: You might have boobed itÂ* - twice, if I am not mistaken! 1. You are using 240V not 230V for your fault current. (Max Ze for a 50A C type is 0.37ohm and remember that is when the cables are at 40 deg) 2. Your resistance calculations should be 16mm earth and 16mm live (unless you wish to chop out the 6mm cpc of the 16mm T&E and not bother using it) Either way you are over the 0.37 ohms allowed. It might be better to swap the head end with some thing like this https://www.tlc-direct.co.uk/Products/CGMSF100.html Yes, it's always better when boobs appear as a pair ;-) I'd done the quick check at 230 but old habits (my fingers initially typed old hobbits) die hard so 240 reappeared when I did the proper check. When I decided to add the 10mm2 cable the brain forgot about the existing CPC. I can't think of an excuse for that :-( As you spotted, there was a third boob in your calcs ... brings back memories of a character from HHG2TTG ;-) I am glad someone like the bit of humour I try to put into some of my posts. The actual fused isolator I was looking for (should you go that route) is the Scolmore DB750. But I am sure the one I linked to is the same thing. Scolmore one here https://www.rselectricalsupplies.co....ched-db750_813 There is a shroud showing on the first link that allows T&E to enter properly. Thanks, but I'm fairly certain that I'm OK with a type C MCB for the sub-main head and type Bs at 16A and 6A in the remote CU. |
#22
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Question about sub-main sizing
On 11/02/2019 19:50, wrote:
On Monday, 11 February 2019 19:12:16 UTC, ARW wrote: On 11/02/2019 11:15, wrote: On 10/02/2019 20:30, ARW wrote: Yes, it's always better when boobs appear as a pair ;-) I'd done the quick check at 230 but old habits (my fingers initially typed old hobbits) die hard so 240 reappeared when I did the proper check. When I decided to add the 10mm2 cable the brain forgot about the existing CPC. I can't think of an excuse for that :-( As you spotted, there was a third boob in your calcs ... brings back memories of a character from HHG2TTG ;-) If there are 3 boobs something is very wrong. NT Have you not heard of Eccentrica Gallumbits, the triple-breasted whore from Eroticon 6? https://hitchhikers.fandom.com/wiki/...ica_Gallumbits |
#23
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Question about sub-main sizing
On 11/02/2019 20:00, wrote:
On 11/02/2019 19:50, wrote: On Monday, 11 February 2019 19:12:16 UTC, ARWÂ* wrote: On 11/02/2019 11:15, wrote: On 10/02/2019 20:30, ARW wrote: Yes, it's always better when boobs appear as a pair ;-) I'd done the quick check at 230 but old habits (my fingers initially typed old hobbits) die hard so 240 reappeared when I did the proper check. When I decided to add the 10mm2 cable the brain forgot about the existing CPC. I can't think of an excuse for that :-( As you spotted, there was a third boob in your calcs ... brings back memories of a character from HHG2TTG ;-) If there are 3 boobs something is very wrong. NT Have you not heard of Eccentrica Gallumbits, the triple-breasted whore from Eroticon 6? https://hitchhikers.fandom.com/wiki/...ica_Gallumbits And good for fine tuning. One for treble, one for bass and one for volume. -- Adam |
#24
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Question about sub-main sizing
On 11/02/2019 11:15, wrote:
As you spotted, there was a third boob in your calcs ... brings back memories of a character from HHG2TTG ;-) Prompting recollection of the tale... So God said unto Eve, "So what do you think of my garden then?" "Oh, its lovely" says Eve, "So pretty, and some many interesting creatures" "And how is the body working out for you, I was quite pleased with that" "Oh I think its rather good... although I am not sure about the third boob" "What do you mean?" "Well the left and the right are ok, they look good and balance nicely, but the middle one just seems to push the others outward, and then they bump into my arms when I swing them as I walk" "Hmmmm, I see what you mean. Here try this" With that a heavenly hand reaches down, grabs the middle boob, and plucks it off with a small squelch, before punting it off into the long grass. A week passes "So Eve, is the new boobie, layout any better" "Oh yes much better!" "So you are happy then?" "Well..." "Go on then spit it out" "I am a bit lonely... I see many of the other animals seem to have mates to play with and for company, but I don't have anyone" "Ah", says God, "I have been working on an idea" "I call it Man. He will be like you only a bit bigger and stronger. He will be able to hunt for you, care for you, defend you, love and cherish you, and be your life long faithful companion, not to mention a few other party tricks I have got in mind. What do you think of that then?" "Oh, God I want one!" "Well there will be a price to pay.... I will need to take a part form your body to start building him" "What do you need, a rib or something?" "Oh no, no need to be so drastic... now let me think" "Where did we put that useless tit?" -- Cheers, John. /================================================== ===============\ | Internode Ltd - http://www.internode.co.uk | |-----------------------------------------------------------------| | John Rumm - john(at)internode(dot)co(dot)uk | \================================================= ================/ |
#25
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Question about sub-main sizing
On 11/02/2019 11:25, wrote:
On 10/02/2019 21:26, John Rumm wrote: On 07/02/2019 19:17, wrote: On 07/02/2019 18:50, Cynic wrote: I've not got tables to hand but check your earth loop impedance against disconnection times for the 40A mcb The sub-main earth loop impedance (20m of 10mm2 and 20m of 16mm2) should be about 60mOhm (37mOhm + 23mOhm) so about 0.4 ohms total (TN-C-S) - about 600A fault current. A type C MCB needs 10x rated current, so 500A for a 50A MCB. Unless I've boobed it should be OK. I think I must be missing something here... where does the 20m of 10mm^2 come into this? Sadly, it was me that was missing something - I'd forgotten about the extg CPC being in parallel with the new single. I must be getting old. Ah, ok, sorry I though I had missed and extra cable somewhere rather than being the extra CPC/Bonding conduction for the submain -- Cheers, John. /================================================== ===============\ | Internode Ltd - http://www.internode.co.uk | |-----------------------------------------------------------------| | John Rumm - john(at)internode(dot)co(dot)uk | \================================================= ================/ |
#26
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Question about sub-main sizing
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#27
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Question about sub-main sizing
On 12/02/2019 09:04, wrote:
On 12/02/2019 02:15, John Rumm wrote: On 11/02/2019 11:15, wrote: As you spotted, there was a third boob in your calcs ... brings back memories of a character from HHG2TTG ;-) Prompting recollection of the tale... So God said unto Eve, "So what do you think of my garden then?" "Oh, its lovely" says Eve, "So pretty, and some many interesting creatures" "And how is the body working out for you, I was quite pleased with that" "Oh I think its rather good... although I am not sure about the third boob" "What do you mean?" "Well the left and the right are ok, they look good and balance nicely, but the middle one just seems to push the others outward, and then they bump into my arms when I swing them as I walk" "Hmmmm, I see what you mean. Here try this" With that a heavenly hand reaches down, grabs the middle boob, and plucks it off with a small squelch, before punting it off into the long grass. A week passes "So Eve, is the new boobie, layout any better" "Oh yes much better!" "So you are happy then?" "Well..." "Go on then spit it out" "I am a bit lonely... I see many of the other animals seem to have mates to play with and for company, but I don't have anyone" "Ah", says God, "I have been working on an idea" "I call it Man. He will be like you only a bit bigger and stronger. He will be able to hunt for you, care for you, defend you, love and cherish you, and be your life long faithful companion, not to mention a few other party tricks I have got in mind. What do you think of that then?" "Oh, God I want one!" "Well there will be a price to pay.... I will need to take a part form your body to start building him" "What do you need, a rib or something?" "Oh no, no need to be so drastic... now let me think" "Where did we put that useless tit?" :-) +1 Now imagine what we could have had if Adam had spared a couple more ribs when Eve was created. Oh, that would be a woman with three tits. -- Adam |
#28
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Question about sub-main sizing
On 12/02/2019 18:48, ARW wrote:
On 12/02/2019 09:04, wrote: On 12/02/2019 02:15, John Rumm wrote: On 11/02/2019 11:15, wrote: As you spotted, there was a third boob in your calcs ... brings back memories of a character from HHG2TTG ;-) Prompting recollection of the tale... So God said unto Eve, "So what do you think of my garden then?" "Oh, its lovely" says Eve, "So pretty, and some many interesting creatures" "And how is the body working out for you, I was quite pleased with that" "Oh I think its rather good... although I am not sure about the third boob" "What do you mean?" "Well the left and the right are ok, they look good and balance nicely, but the middle one just seems to push the others outward, and then they bump into my arms when I swing them as I walk" "Hmmmm, I see what you mean. Here try this" With that a heavenly hand reaches down, grabs the middle boob, and plucks it off with a small squelch, before punting it off into the long grass. A week passes "So Eve, is the new boobie, layout any better" "Oh yes much better!" "So you are happy then?" "Well..." "Go on then spit it out" "I am a bit lonely... I see many of the other animals seem to have mates to play with and for company, but I don't have anyone" "Ah", says God, "I have been working on an idea" "I call it Man. He will be like you only a bit bigger and stronger. He will be able to hunt for you, care for you, defend you, love and cherish you, and be your life long faithful companion, not to mention a few other party tricks I have got in mind. What do you think of that then?" "Oh, God I want one!" "Well there will be a price to pay.... I will need to take a part form your body to start building him" "What do you need, a rib or something?" "Oh no, no need to be so drastic... now let me think" "Where did we put that useless tit?" :-) +1 Now imagine what we could have had if Adam had spared a couple more ribs when Eve was created. Oh, that would be a woman with three tits. I thought He was going to say 'I know - you have a brain - you never use that, we will make him out of that!' -- €œIdeas are inherently conservative. They yield not to the attack of other ideas but to the massive onslaught of circumstance" - John K Galbraith |
#29
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Question about sub-main sizing
On 12/02/2019 19:33, The Natural Philosopher wrote:
On 12/02/2019 18:48, ARW wrote: On 12/02/2019 09:04, wrote: On 12/02/2019 02:15, John Rumm wrote: On 11/02/2019 11:15, wrote: As you spotted, there was a third boob in your calcs ... brings back memories of a character from HHG2TTG ;-) Prompting recollection of the tale... So God said unto Eve, "So what do you think of my garden then?" "Oh, its lovely" says Eve, "So pretty, and some many interesting creatures" "And how is the body working out for you, I was quite pleased with that" "Oh I think its rather good... although I am not sure about the third boob" "What do you mean?" "Well the left and the right are ok, they look good and balance nicely, but the middle one just seems to push the others outward, and then they bump into my arms when I swing them as I walk" "Hmmmm, I see what you mean. Here try this" With that a heavenly hand reaches down, grabs the middle boob, and plucks it off with a small squelch, before punting it off into the long grass. A week passes "So Eve, is the new boobie, layout any better" "Oh yes much better!" "So you are happy then?" "Well..." "Go on then spit it out" "I am a bit lonely... I see many of the other animals seem to have mates to play with and for company, but I don't have anyone" "Ah", says God, "I have been working on an idea" "I call it Man. He will be like you only a bit bigger and stronger. He will be able to hunt for you, care for you, defend you, love and cherish you, and be your life long faithful companion, not to mention a few other party tricks I have got in mind. What do you think of that then?" "Oh, God I want one!" "Well there will be a price to pay.... I will need to take a part form your body to start building him" "What do you need, a rib or something?" "Oh no, no need to be so drastic... now let me think" "Where did we put that useless tit?" :-) +1 Now imagine what we could have had if Adam had spared a couple more ribs when Eve was created. Oh, that would be a woman with three tits. I thought He was going to say 'I know - you have a brain - you never use that, we will make him out of that!' VBG. -- Adam |
#30
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Question about sub-main sizing
On Monday, 11 February 2019 20:00:33 UTC, wrote:
On 11/02/2019 19:50, tabbypurr wrote: On Monday, 11 February 2019 19:12:16 UTC, ARW wrote: On 11/02/2019 11:15, wrote: On 10/02/2019 20:30, ARW wrote: Yes, it's always better when boobs appear as a pair ;-) I'd done the quick check at 230 but old habits (my fingers initially typed old hobbits) die hard so 240 reappeared when I did the proper check. When I decided to add the 10mm2 cable the brain forgot about the existing CPC. I can't think of an excuse for that :-( As you spotted, there was a third boob in your calcs ... brings back memories of a character from HHG2TTG ;-) If there are 3 boobs something is very wrong. NT Have you not heard of Eccentrica Gallumbits, the triple-breasted whore from Eroticon 6? https://hitchhikers.fandom.com/wiki/...ica_Gallumbits I still say if you meet her something is very wrong NT |
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