New sub board for shed swa advice.

[Jcamerz]

Hi guys new to the forum after bit of advice. My family are installing a new shed in the garden and require a lot of power ie few sockets, lights. I am planning of running a swa fed from 32a mcb from the main board to a sub board.
Have a question-
Shall I install the new 32a mcb in the main board on the RCD side or main switch side?
Thanks

 

[Octopus]

there are two threads of conversation - the smaller one is about which earthing system you can connect to. I have pinched the typed up version of the reg but the answer is it has to be the same earthing system as the installation containing the protective device
"542.1.3.3 [...]if the protective conductor forms part of a cable, the protective conductor shall be earthed only in the installation containing the associated protective device."

But it still doesn't say which ends it should be connected ....

 

[Octopus]

there are two threads of conversation - the smaller one is about which earthing system you can connect to. I have pinched the typed up version of the reg but the answer is it has to be the same earthing system as the installation containing the protective device
"542.1.3.3 [...]if the protective conductor forms part of a cable, the protective conductor shall be earthed only in the installation containing the associated protective device."

But it still doesn't say which ends it should be connected ....

 

[telectrix]

there are two threads of conversation - the smaller one is about which earthing system you can connect to. I have pinched the typed up version of the reg but the answer is it has to be the same earthing system as the installation containing the protective device
"542.1.3.3 [...]if the protective conductor forms part of a cable, the protective conductor shall be earthed only in the installation containing the associated protective device."

but the argument is not about earthing the protective conductor, is it? it's about earthing the armour when said armour is not used as cpc.

 

[netblindpaul]

So, EAWR requires that any conductor that may become "inadvertently charged" must be suitably earthed, my wording, the original is earlier in the thread.
If, EAWR does not apply to installations under BS 7671 why is this contained there in?
The Health and Safety Executive (HSE) welcomes the publication of BS 7671:2018, Requirements for Electrical Installations, IET Wiring Regulations 18th Edition. BS 7671 and the IET/IEE Wiring Regulations have been extensively referred to in HSE guidance over the years. Installations which conform to the standards laid down in BS 7671:2018 are regarded by HSE as likely to achieve conformity with the relevant parts of the Electricity at Work Regulations 1989. Existing installations may have been designed and installed to conform to the standards set by earlier editions of BS 7671 or the IEE Wiring Regulations. This does not mean that they will fail to achieve conformity with the relevant parts of the Electricity at Work Regulations 1989.

 

[Deleted member 26818]

So if this is true and the installation does not comply with EAWR, how does the installer comply with HASAWA Reg 3?

What installer?

 

[netblindpaul]

Any installer anywhere.

 

[Deleted member 26818]

Any installer anywhere.

Right now, I’m sat in my bungalow.
I cannot (unless I look in a mirror) see any installers.
Why would my electrical installation have to comply with EAWR or HASAWA?

 

[netblindpaul]

Right now, I’m sat in my bungalow.
I cannot (unless I look in a mirror) see any installers.
Why would my electrical installation have to comply with EAWR or HASAWA?

Someone installed the work, and if they did this as part of a business, which we are discussing, not DIY, then the installation works and the requirement for compliance with EAWR of the installation was there when it was installed, thus the installer was required to comply with the law of the land as per EAWR & HASAWA.
What happened after that with regard to DIY is not relevant and has not been discussed.
So if you did your own install in your own home that is not relevant, but, if you are employed or self-employed then EAWR and HASAWA applied at the time of the install, and thus the installation must comply with the law.

 

[davesparks]

Ok, how about a supply to an outside socket or shed where you're coming from an existing socket on a RFC, plasterboard walls so you put in a single dry lining box for a DP switch or SFCU and drill through to outside behind the box, how do you earth the armour at that termination ? Yes I know you could terminate into a box outside but why create another unnecessary connection when you can earth the armour at the other end ? Or you could have an insulated CU to take your SWA from with no space around it for an additional connection box and no way of drilling a 20mm hole into it.

But you will still be terminating the SWA with the correct gland so I see no reason not to swap the locknut for an earthing nut.
Or are you suggesting that it’s ok to terminate SWA without a gland?

 

[davesparks]

So you may end up with a metal consumer unit connected to a TT arrangement with a Zs of up to 1667 ohms for example, fitted adjacent to a metal adaptable box to which the swa is terminated with a Zs of perhaps .35 ohms. Is that right?

No you wouldn’t, you can’t have exposed metal connected to two different earthing systems like that. You insulate the armour at the load end of the submain so that it does not introduce another potential.

Also leaving a TT system with such a high Ra is unacceptable.

 

[davesparks]

But it still doesn't say which ends it should be connected ....

No it doesn’t say specifically which end of an SWA cable must be earthed if it is done at only one end, it says what must be achieved by the earthing. These regulations assume that we have enough sense to apply them correctly and don’t need a step by step guide to every little detail.

So the regulation basically says that the armour must be earthed to prevent it becoming charged (either through induction, capacitance or touching something which is live) in normal service or under fault conditions.

In normal service it wouldn’t matter which end is earthed, however under fault conditions such as physical damage it is possible that several armour strands could be broken. This could lead to the armour on the live side of the damage being unearthed if the connection was only made at the load end.

 

[Pete999]

but the argument is not about earthing the protective conductor, is it? it's about earthing the armour when said armour is not used as cpc.

Precisamundo

 

[Deleted member 9648]

No it doesn’t say specifically which end of an SWA cable must be earthed if it is done at only one end, it says what must be achieved by the earthing. These regulations assume that we have enough sense to apply them correctly and don’t need a step by step guide to every little detail.

So the regulation basically says that the armour must be earthed to prevent it becoming charged (either through induction, capacitance or touching something which is live) in normal service or under fault conditions.

In normal service it wouldn’t matter which end is earthed, however under fault conditions such as physical damage it is possible that several armour strands could be broken. This could lead to the armour on the live side of the damage being unearthed if the connection was only made at the load end.

If you are going to use that as an argument for earthing at both ends then you would have to apply the same argument to all radial circuit cpc's as damage may result in partial or complete loss of earth to part of the circuit.
Not all scenario's are sufficiently likely to be worth allowing for.

 

[Deleted member 26818]

If you are going to use that as an argument for earthing at both ends then you would have to apply the same argument to all radial circuit cpc's as damage may result in partial or complete loss of earth to part of the circuit.
Not all scenario's are sufficiently likely to be worth allowing for.

Exactly why high integrity earthin requires a second CPC.

 

[Deleted member 9648]

Exactly why high integrity earthin requires a second CPC.

Don't think earthing a cables conductive part is classed as requiring high integrity earthing.