Yes that's correct. If there is no RCD protection then a line to earth fault such as mechanical damage to the SWA will not automatically disconnect the circuit, and that's a bad thing™
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- Thread starter xr4x4
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Correct. Normally SWA does not require RCD protection as due to it's construction it is difficult to damage, and if you do manage to cut through to the live conductors, you will cause a short between the earthed metal surrounding the conductors and one or more of the lives, which will blow the fuse protecting it. This is know as "automatic disconnection of supply". It is a fail safe cable.
If you did the same on a TT supply without an RCD, due to the high impedence of an earth electrode, the current flowing from line to earth would not be big enough to blow the fuse and the cable would stay live. If there is an RCD fitted, this will detect the fault and acheive "automatic disconnection of supply"
If you did the same on a TT supply without an RCD, due to the high impedence of an earth electrode, the current flowing from line to earth would not be big enough to blow the fuse and the cable would stay live. If there is an RCD fitted, this will detect the fault and acheive "automatic disconnection of supply"
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Ok, as per my other thread, 'going PME'
If we do go PME, i can do the same as planned (at beginning of post) but just drop the 100ma TD RCD?
I.E leave our install well alone, protected by a 30ma RCD, remove SWAs and relocate them externally into a mini IP rated CU and enclosure, swa protected with mcbs, 30ma RCD CUs at other ends?
If we do go PME, i can do the same as planned (at beginning of post) but just drop the 100ma TD RCD?
I.E leave our install well alone, protected by a 30ma RCD, remove SWAs and relocate them externally into a mini IP rated CU and enclosure, swa protected with mcbs, 30ma RCD CUs at other ends?
That sounds correct to me.
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Hope there are no metallic enclosures fed by unprotected tails.
It's more common to use switchfuse(s).
It's ok as the supply will be TN-C-S and not TT anymore.
Yes, it would be better to use either switch fuses or an IP rated CU as the OP mentioned, but fit it with HRC fuses rather than MCBs
nope, meter, henleys, tails straight into CU.
Ok, been thinking.
Southern electric have been out today to check the poles, he called and said he wanted to get in to do a earth loop test, but i couldn't be there, so he said they would arrange for another day.
Im thinking if we can go PME, i don't need to have an external box for the RCD. I could still get the SWA supplies separated in the cupboard into a separate CU (or other).
Im just trying to think of a fault that would trip the OCPD and would need someone to access the cupboard and all i can think of is if the SWA got cut!
So how does this sound, if we do get converted to PME?
Inside our meter cupboard, tails from meter into henleys, one split back into our RCD and CU, leaving this install intact.
Other tails into a separate CU with 3 MCBs of suitable size for SWA cables and terminate the swa back into the new cu.
The only point maybe that the SWAs need to be installed into adaptable boxs to extend them to the new CU.
Thoughts?
Southern electric have been out today to check the poles, he called and said he wanted to get in to do a earth loop test, but i couldn't be there, so he said they would arrange for another day.
Im thinking if we can go PME, i don't need to have an external box for the RCD. I could still get the SWA supplies separated in the cupboard into a separate CU (or other).
Im just trying to think of a fault that would trip the OCPD and would need someone to access the cupboard and all i can think of is if the SWA got cut!
So how does this sound, if we do get converted to PME?
Inside our meter cupboard, tails from meter into henleys, one split back into our RCD and CU, leaving this install intact.
Other tails into a separate CU with 3 MCBs of suitable size for SWA cables and terminate the swa back into the new cu.
The only point maybe that the SWAs need to be installed into adaptable boxs to extend them to the new CU.
Thoughts?
As long as you've got sufficient discrimination between the device the one(s) in the outbuildings. A good reason to use switchfuses.
Hopefully your electrician will have the gumption to use metal enclosures.
I dont think theres room for 3 switch fuses and i cant see the advantage.
I would also assume he would use the same size as the current MCBs, as these have always seemed to work ok and never tripped.
Also, i cant see the advantage of using metal enclonsures? As long as the SWA is earthed, i dont see a problem with using either.
Fair enough, but it's your electrician who will be deciding what to use, not you or I.
Fair enough, but it's your electrician who will be deciding what MCB ratings to use, not you or I.
Fair enough, but it's your electrician who will be terminating the SWA, not you or I.
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