Garage Wiring- The Plan

[BigWallop]

If the safety breaker used in the new isolator switch is of an RCD design, then the housings can be metal clad at both ends of the new sub-mains supply. There is no need to insulate using things made of plastic in between the new consumer unit and old installation. The OP (FreddieLives) should know what types of safety breaker devices to use on this type of sub-mains installation or he shouldn't be touching it at all, in my opinion.

A new earth spike at the out-house would protect both the new SWA supply and the garage CU without interfering with the existing house system. The only connections made inside the house would be the tails and Henley blocks from the meter to a new isolator switch with a properly rated safety breaker device in-built.

The earth fault loop impedance would not have to bring the new installation to the same potential as the house, as the new supply and garage installation would become a totally separate entity from everything around it. So there would be no need to install equipotential bonding or insulated anything between all parts of the old and new systems. The new earth spike at the garage would be between the sub-mains cable and the out-house consumer unit, and would mean a more secure method of fault detection for all of the new system. If done properly, then the SWA cable and new consumer unit and wiring system in the out-house would share the same earth fault protection between them.

Nothing over complicated in it, and all safe.

[BigWallop]

And you not fully understanding my reply, shows that you have? Anyone asking the type of question that is being asked in this instance, should already know how to design safety into the type of sub-mains supply layout I have given. If they don't, then they shouldn't be touching it at all in my opinion.

I don't know what type of loading is being applied to this installation, so I have also not given any advice on the gauge of cable to be used. I have only advised on a style of cable suitable for this type of installation. Does this also mean I don't have any qualification on this type of works? I have also not supplied any techincal details on the earth fault loop design, and only advised on a suitable position for it to placed. So I take it, in your view, this also means I'm not qualified?

I'm not holding the hand of the person that is attempting this project, so I can't say anything more technical than give advice on how I think the layout should be made and without over complicating the whole thing. So this makes me un-qualified to make suppositions on how the final design should take into account the loadings they wish to apply, or on the safety devices they must use in their final design. I'm not doing the job for them, so I'm un-qualified to give any more advice on the works unseen.

If you think you can give anymore advice on this unseen project by using your telepathic skills, then by all means go ahead. If you know more than I do about the loadings that the OP will be applying to this new sub-mains installation, then do not hesitate to continue to tell them which specific products they must use.

If you are as much in the dark about the full details as everyone else is, then shut the hell up and don't cast aspersions on people you know nothing about. Now f*ck off little boy, before you make me angry. I do not have to deem myself to you, or any other, on my personal qualifications or skills.

[Doctor Drivel]

This Pillock thinks conduit is dangerous, yet leaves his boiler unserviced for 18 years. Some mothers......

[Doctor Drivel]

Of course there is. The garage CU will have over current protection for each circuit. The total load of the garage CU should not exceed the limits of the SWA cable.

[Doctor Drivel]

I don't like it, but it is done, ana safe, within regs, and I have seen a number of them on new houses. An unswitched spur is inserted into the downstairs ring on an outside wall, then an armoured cable out through the wall to the garage.

[Andy Hall]

Dangerous nonsense.

1) The overcurrent protection for a length of cable needs to be at the supply end.

2) It is normal for the total potential load of a set of circuits on a CU to exceed the supply capacity - common practice in house main CUs for example.

Stick to hacksawing plastic pipes. At least you are reasonably unlikely to cause death through electrocution or fire.

[Doctor Drivel]

What crap. The ring has an over-current mcb, so the ring CANNOT be run more than what the cables on the ring is rated. If it exceed supply capacity the mcb trips in. Boy are you dumb.

..Lord Hall doesn't know, a man who has no clue ..he has no clue about the things which are known to me and you

..24/7 he is vacant within his head ..no knoweldge, reason, logic, this must be said

..drivel and babble just comes so ..relentless, incoherrent in its flow

..it's time take no notice of this hot head babbling fool ..just laugh and smile and thank the Lord you are sane and cool

[Phil]

OC prtoection for the cable has to be at source - you 'fuse down' to protect the cable....the individual cct protection in the garage is to protect the devices plugged in - not the cable to the house.

[Andy Hall]

1) Your proposal was that the garage CU and MCBs therein protects the cable. It doesn't. 2) Are you proposing running a ring to the garage now?

The correct way is to install a separate circuit from the main house CU or main supply with correct circuit breaker fitted to it.

A poorer practice alternative is to run from a ring circuit but via a suitable overload protection.

25 Yorkshire elbows please.

[Doctor Drivel]

It does if the main garage CU isolating switch is rated under the supply cable rating. Which I drew cautioned.

You are making things up again.

For light use yes. One was proposing a separate supply after the meter. That may be OK for heavy use, and easier for separate metering.

I mentioned that. Boy are you slow.

[Andy Hall]

It does not.

What happens if the cable is shorted before the garage CU?

It's what you said

It's good practice anyway.

[Doctor Drivel]

The same thing that happens if the cable is shorted before the CU of the house.

I never. But there is no reason not to if the mcb in the garge CU is rated accordingly.

What is?

[Andy Hall]

The main electricity supplier fuse goes?

You said, and I quote:

"The ring has an over-current mcb, so the ring CANNOT be run more than what the cables on the ring is rated. If it exceed supply capacity the mcb trips in"

Installing a separate ciruit with a breaker providing overcurrent protection for the cable to the garage.

[John Rumm]

I Don't dispute that...

Not immediatly dangerours unless issues relating to the extension of the equipotential zone are not also followed, but not as good as if done correctly.

Nope. We have had this discussion before. If you insist I can quote chapter and verse of the regulations is falls foul of.

If you were dealing with an attached garage that is effectively part of the house (i.e inside connecting door etc) then there is nothing stopping you extending the socket ringl final circuit into the garage, and the downstairs lighting circuit likewise. No need for the FCU.

If you are talking about a detached building then it is a lash up for various reasons.

[John Rumm]

"safety breaker" is a non standard term. I would suggest that if you are going to offer advice in this area you be a little more specific with your terminology, since subtle misunderstandings can make big differences.

You need to decide if the garage is going to be part of the PME system with associated implications, or a standalone TT system. If it is TT then you do not want any connectivity between house earth and the TT earth. Hence the need for an insulated CU (or a metal clad one and insulating glands etc). You seem to be advocating some mixture of both.

? The OP (FreddieLives)

Wow!, what a cop out. What is the point in posting half the solution, and expecting the OP to guess which bits you missed out?

Note sure what you mean by "interfering with the existing house system" in this case. Could you clarify?

An isolator switch is just that. It includes no overcurrent protection. Unless you mean a switchfuse, or a CU, in which case it is better to be specific I would suggest.

Woa, there boy! Your speaking bollox. What has earth fault loop impedance go to do with bringing "the new installation to the same potential as the house"?

Again - you need one or the other. If separated (i.e. TT) in the outbuilding then don't join the earths. If part of the PME system, then do the required bonding.

What do you mean by "between"?

[John Rumm]

Since the only "ring" here is presumably one in the outbuilding, then you are correct (allthough not relevent). The MCB for that circuit will protect the cables of the circuit. However we are not talking about that cicruit, but the sub main feed to the CU that supplies it. The overcurrent protection is needed for this to cope with two eventualities:

Firstly when the total load of the garage CU (i.e. all circuits combined) exceeds the sub main cable capacity, and secondly, when a fault affects the sub main cable before the garage CU (i.e. damage to the cable itself or a fire in the garage etc).

Those in glass houses ought not throw stones....

[Doctor Drivel]

I saw it and questioned it, and was assured it was fully within. No electrical man has countered when presented. Mopst say back top the CU and its own mcb, but apart from that the same, as these garages were just spured off a ring.

Please do, and tell when the reg came about. 3-core cable was taken to the garages from a switchless spur, with 13 A fuse off the downstairs ring.

It was the most convenient point of take off. Otherwise the cable had to go an extra 20 - 30 foot and enter the building via the mains cable duct to the CU, or a separte duct. One light and one double socket in the garage, pretty standard. The garage CU was a MEM Numera 2000 with two fuses, not mcb's, of 5A and 15A. A 100A breaker was also fitted in the MEM. Protection in the garage is via the fuses alone, as I can't see that 100A main garage CU breaker does anything, being off a 30A RCD'd house ring. The RCD would cut in before the fuses had a chance to blow.

So the fuse in MEM, the fuse in the switchless spur, the mcb at the CU and the RCD. Then the Plugtop fuse as well when using an appliance. Seems well protected

[Doctor Drivel]

I thought of you.

The cable from the meter to the garage CU should be sized to suit. Obvious. The garage CU total protection should not allow loads above the supply cable capacity. This is the same for the main house supply cable and CU.

Lord Hall was on about rings quite often exceeding the load capacity and getting away with it. That is nonsense. The rings two cables are rated above the mcb on that circuit. So they cannot be exceeded.

[Andy Hall]

You have it the wrong way round.

The house end circuit breaker should not allow loads over the cable carrying capacity.

What you have said is nonsense.

What I said is that it is common practice for the sum of the circuits and breakers protecting them installed in a CU to exceed the capacity of the circuit feeding said CU. This is one of the principles of diversity.

The only exception is that the CU itself must not have the principles of diversity applied to it.

Irrelevant.

[BigWallop]

eventualities:

Two 2.5 mm csa' cables make a total cross sectional area of 5 mm. The breaker normally used on a ring final circuit is 30 (32) Amps rated. This current rating is to high for a cable of cross sectional area of 5 mm. Specially so if the ring final circuit is rather long. It is called diversity and takes into account that not all points on the ring final circuit will be used at full load at all times. So you are telling us this can't be done?

The diversity guide also applies to the mains supply conductors, but these must be protected separately at their source by their own automatic breaker devices. This ensures that the supply is broken in the event of a fault on the supply. The mains conductors can not rely on the breaker devices in the consumer unit that they supply.