How about a Small 3 way Consumer unit! Socket Light & Small Heater
Log cabin 6mm 4 core swa
- Thread starter sparcktikus
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Although Autumn 2005 this gives basics it talks about if TN-C-S or TT and goes through why one selects either.
In a square of houses in a housing estate where the garden is surrounded by houses, then same earth as house, unless used as a radio shack, but where there are no houses further on than shed one must consider the possible voltage gradient.
Also one must consider with a TN-C-S supply what will happen if the combined earth/neutral is lost, I have seen 4 mm² reduced to copper balls on the drive after it melted, OK rather a good earth at shed (radio shack) but you must use your vast experience to decide in each case which is best. Can't be done on a forum, it needs the person on site to decide best option.
The death of Emma Shaw showed how asking a group of lads what to do in works canteen does not work, remember no fuse or MCB protects the earth wire, it is all down to the earth loop impedance.
In a square of houses in a housing estate where the garden is surrounded by houses, then same earth as house, unless used as a radio shack, but where there are no houses further on than shed one must consider the possible voltage gradient.
Also one must consider with a TN-C-S supply what will happen if the combined earth/neutral is lost, I have seen 4 mm² reduced to copper balls on the drive after it melted, OK rather a good earth at shed (radio shack) but you must use your vast experience to decide in each case which is best. Can't be done on a forum, it needs the person on site to decide best option.
The death of Emma Shaw showed how asking a group of lads what to do in works canteen does not work, remember no fuse or MCB protects the earth wire, it is all down to the earth loop impedance.
Assuming they are all on the same Neutral. My cottage on a street corner and the adjacent retail unit have different Neutrals from different cables from the substation. The common water supply has to have an isolation section to prevent the two CPCs becoming connected to each other.
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How about the facts that there's nothing wrong with it and that it allows RCD protection to be local.
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No required. As I said sockets direct (using MCB in house). Light(s) via switched FCU, and yes heater can be plugged into one of the sockets.
I came across a few comments from electricians that mention rusting of SWA armour, in the iet forum.
They were saying they had come across this issue in the course of their work, which led them think maybe it was better to use one of the conductors as an earth in preference. I get the impression earth sizing is sometimes misunderstood and that some people choose to fit an SWA cable with an extra core to use as the earth rather than calculate with the adiabatic equation whether the armour would be suitable.
Winston overlooks the problem that a fault in the cabin could trip MCB and/or RCD in the house leaving people in the house in the dark.
I can not believe you're actually trying to defend this idea - you're literally on your own with this one!
The SWA must always be earthed. Whether or not it is being used as the cpc or part of it is irrelevant. The average bodger will know it is cheaper and quicker to use a couple of plastic stuffing glands, rather than brass compression glands. And will use the rust idea as some twisted excuse to carry on bodging,
I can understand having no cu in a lash up shed, but if someone is going to the effort of some thick swa, may as well have a metal cu to terminate it to.
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It is possible to take the feed from a RBCO in the house, and use a switched FCU for the lights, however once you want over 13 amp in the out building either RBCO in house or CU in outbuilding, the option of a simple MCB in the house is only valid if supply under 13A so a RCD FCU in house or outbuilding can be used.
There is a case where there is no option for a MCB or RBCO in the house CU where it is protected by the house RCD, where only option is an isolator in the house or outbuilding, not ideal but either one end or other of the SWA you want option to turn off both live supplies, unlikely SWA will be damaged, so although could be either end, likely installed in outbuilding, however the housing for the isolator is very similar to a CU so may as well be a CU. Only it would not need a RCD in the unit.
As to metal or plastic, the question is when is a CU not a CU? Answer if anything is altered that is not authorised by the manufacturer, it then becomes a distribution unit, in theory if in the control of an ordinary person a distribution unit has to be type tested, but the designer, installer and inspection and tester can hardly be classed as a ordinary person.
So we return to a scheme member electrician working on your home, is more limited than your self, as to how a court would view what you have done no one knows, and unless there is a death unlikely it would go to court.
The MCB/RCD/RCBO in the house does not need to be the same one as the rest of the house.
If its the only cpc, I imagine severe rusting would create an unprotected installation. It does sound though from what you say, that maybe its an excuse for a bodge.
It seems anazing anybody wouldnt use brass glands, they are only a few quid.
It can be a problem. Assume some minor damage to the outer sheath of the cable allowing ground water to reach the steel wire.
When the steel wire is connected to the MET in a PME system the steel wire will be at Neutral potential which may be a few volts different to the ground water in contact with the steel wire. AC galvanic corrosion will occur.
When the steel wire is connected to the MET of a TT system with a copper ground rod there will be a voltage generated from the cell created from dis-similar metals in electrolyte. Ground water being the electrolyte. DC galvanic corrosion will occur. Also happens if there is a lead water pipe or other metallic item that is buried and connected to the MET.
Acidic ground water is another cause of corrosion.
The rate of corrosion may be very slow but over time and with all the corrosion in the same area of the cable ( where the sheath has been damaged ) the risk of loss of adequate continuity is significant.
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