Intended departure from the Regs

[happysteve]

As the designer of an installation, anyone put their name against an intended departure from the Regs (120.3)? If so, and you're willing to share, what were the circumstances?

Just wondering how common/rare this is.

Cheers!

 

[Leesparkykent]

I suppose using a non standard cable like SY as part of the fixed installation but as the designer you consider the cable, installation method etc affords the same level as safety as compliance.

 

[happysteve]

I've done one:

Does not comply with 521.5.1 (ferromagnetic enclosures: electromagnetic effects). Earthing conductor enters steel enclosure separate from supply. PEFC <10A (TT; Ra ~30Ω; nothing extraneous), upstream OCPD 20A BS EN 60898 type B: no risk of EM effects.

~tin hat on~

 

[Leesparkykent]

I've done one:

View attachment 38611
Does not comply with 521.5.1 (ferromagnetic enclosures: electromagnetic effects). Earthing conductor enters steel enclosure separate from supply. PEFC <10A (TT; Ra ~30Ω; nothing extraneous), upstream OCPD 20A BS EN 60898 type B: no risk of EM effects.

~tin hat on~

Haven't got my BYB to hand but I'm sure reg 521.5.1 permits the use of a separate protective conductor to be run in parallel with an SWA cable.

 

[happysteve]

It does. (Good memory!) The provision is for an additional protective conductor in parallel with the armour of SWA to enter the enclosure separate from the SWA. The earthing conductor is not in parallel. The armour is earthed only in the installation containing the OCPD (which is TN-C-S).

 

[Wilko]

Agree with Lee - I think this arrangement may fall into the last para of that reg "It is permitted for such an additional conductor to enter the enclosure individually".
And, if I read the reg slightly differently, the SWA armour is the "appropriate protective conductor" for that circuit, and if it enters it should enter with the lives. But the earthing conductor for the TT installation is a different item altogether from the supply circuit protective conductor and so it may enter where it needs. Or is that stretching ?
Good looking job HS !

 

[Gavin John Hyde]

Good looking job HS !

Couldn't have said it better myself. Nice to see a job well presented and people still using metal conduit on a domestic job... people seem to have fallen in love with horrible black plastic around here.

 

[freddo]

Who is Tom?

 

[Wilko]

Who's Tom?

One Lucky Guy ...

 

[Darkwood]

Departure from the regs is not as uncommon as may be thought from a deliberate intent perspective, the regulations are a guidelines and not law enforced although if you do digress from them you need to know your stuff and the materials your using down to the manufactures limitations. The BS7671 is a broad guideline and is suited to most in the industry and gives them somewhat a protective shield if ever the need should arise but it can not account for all the circumstances and situations out there, if you can ensure and provide a risk assessment for a departure from the regs that safety is not impaired and material used are adequate for their use and environment then it is acceptable to digress from the BS7671.
Doing it without reflecting on your position or considering the consequences if things go wrong is where you have to realise that you tread a fine line when departing from said regulations.

 

[Darkwood]

As goes the above query then you are not understanding how eddie currents work in metal enclosures, the earth will be strapped down to the enclosure if it was metal regardless where it enters, it becomes and issues not in domestic but at 100amp load plus where you take polyphase through separate holes, technically the regs apply across the board but the issue at domestic level are rarely of any practical concern.