Garage Supply

[GH Elec]

Hi all.

I’m a qualified electrician but haven’t had loads of experience doing domestic work so need some advice please.

The current consumer unit has no spare ways and she doesn’t want it upgraded.

I was going to install a 5 Way Henley block with 16mm tails for my new supply. I’m hearing different things on what to install. Originally I was going to put a DP Wylex Isolator in and run my 6mm 3 core SWA from that to a new Garage board, which will have an RCD and a 32a MCB and a 6a MCB.

However the wholesalers have sent me a 100 Fuse Switch. (Image attached) My friends at work have said this will be fine. But other people have told me that I need an RCD at both ends. So a Garage board with an RCD and 40a MCB at the meter end.

Also regarding the earths it’s a TNS system. The garage is only 15 metres away from the meter, can I just come off the existing MET for the garage earth. Or will a earth rod need to be installed.

Any advice will be much appreciated

 

[xylophone]

Providence or order code mix up has substituted an isolator that gives no protection to your 6mm SWA with a switch fuse which can. You will need a smaller fuse than 100A I think to protect the SWA but it sounds good IMHO.

 

[Midwest]

I've fitted both, similar one switch fuse to yours and the Wylex. Wylex was marginally better.

Why would an swa cable require RCD protection, and why put two RCD in series? Two fuses in series, whose guess which would go first, but if your head is 100A, suppose it would make sense to put in a lower one for your new supply to garage.

Is there any extraneous conductive parts in the garage? How are you going to manage the notification process, if you don't do domestic work?

 

[buzzlightyear]

if there is no room in the in ,then stick one way board and from there to new garage unit .
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can I just come off the existing MET for the garage earth.

yes ,and no earth rod.considering is a tns. read guideance note 8

 

[Strima]

32A for sockets in the garage? What are they growing in small quantities?

I would probably go for 40 amp BS88 at source in the switched fuse, this will give better discrimination in the event of a fault.

No need for RCD protection on the SWA. Only final circuits will need additional protection.

 

[GH Elec]

Providence or order code mix up has substituted an isolator that gives no protection to your 6mm SWA with a switch fuse which can. You will need a smaller fuse than 100A I think to protect the SWA but it sounds good IMHO.

Yeah it has come with a 100A/80A/60A fuse. So depending on the main fuse I’ll put a lower one in to suit. Thanks xylophone
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I've fitted both, similar one switch fuse to yours and the Wylex. Wylex was marginally better.

Why would an swa cable require RCD protection, and why put two RCD in series? Two fuses in series, whose guess which would go first, but if your head is 100A, suppose it would make sense to put in a lower one for your new supply to garage.

Is there any extraneous conductive parts in the garage? How are you going to manage the notification process, if you don't do domestic work?

Oh so either way works. In future I think I’ll go with the Wylex DP Ioslator. The RCD is there to protect the SWA no? Yh I was going to put a lower fuse in to what’s in the head.

The garage door, which I’ll earth. Thanks Midwest
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if there is no room in the in ,then stick one way board and from there to new garage unit .
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yes ,and no earth rod.considering is a tns. read guideance note 8

Ok thanks Buzzlightyear

 

[Midwest]

Yeah it has come with a 100A/80A/60A fuse. So depending on the main fuse I’ll put a lower one in to suit. Thanks xylophone
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Oh so either way works. In future I think I’ll go with the Wylex DP Ioslator. The RCD is there to protect the SWA no? Yh I was going to put a lower fuse in to what’s in the head.

The garage door, which I’ll earth. Thanks Midwest

The swa doesn’t need RCD ‘protection ‘. Why do you think the garage door needs bonding (it’s not gonna be earthed)?

 

[telectrix]

your SWA needs protecting with a 40A fuse in the isolator. it does not require RCD; as long as you ensure the armour is earthed at supply end. the armour may be used as cpc for the garage sub. no rod needed.

 

[GH Elec]

The swa doesn’t need RCD ‘protection ‘. Why do you think the garage door needs bonding (it’s not gonna be earthed)?

32A for sockets in the garage? What are they growing in small quantities?

I would probably go for 40 amp BS88 at source in the switched fuse, this will give better discrimination in the event of a fault.

No need for RCD protection on the SWA. Only final circuits will need additional protection.
[/

The swa doesn’t need RCD ‘protection ‘. Why do you think the garage door needs bonding (it’s not gonna be earthed)?

Right ok. And the state of the install in the garage I’m assuming no. But until I start uncovering I won’t know.

The swa doesn’t need RCD ‘protection ‘. Why do you think the garage door needs bonding (it’s not gonna be earthed)?

Right ok. And the state of the install in the garage I’m assuming no. But until I start uncovering I won’t know.

 

[telectrix]

you only need to bond the door if it's proven to be extraneous. i.e. resistance <0.02 Meg to MET ( using IR tester).

 

[Midwest]

you only need to bond the door if it's proven to be extraneous. i.e. resistance <0.02 Meg to MET ( using IR tester).

Which I’ll wager it’s not.
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Right ok. And the state of the install in the garage I’m assuming no. But until I start uncovering I won’t know.

Errgh?

 

[GH Elec]

your SWA needs protecting with a 40A fuse in the isolator. it does not require RCD; as long as you ensure the armour is earthed at supply end. the armour may be used as cpc for the garage sub. no rod needed.

Ok thanks telectrix
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Which I’ll wager it’s not. ☺
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Errgh?

There’s existing install there already, twin and earth supply on a washing line. Awful.
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you only need to bond the door if it's proven to be extraneous. i.e. resistance <0.02 Meg to MET ( using IR tester).

Ok thanks for the info telectrix
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your SWA needs protecting with a 40A fuse in the isolator. it does not require RCD; as long as you ensure the armour is earthed at supply end. the armour may be used as cpc for the garage sub. no rod needed.

Although it doesn’t need an RCD in the garage. If I’ve got a garage board that’s got an RCD is it going to be detrimental putting it in?

 

[telectrix]

you need RCD in garage board. it will be the only one on your installation.

 

[GH Elec]

you need RCD in garage board. it will be the only one on your installation.

Yeah ok I’m with you. Last question I promise, with the earth. I’ve got a 3 core SWA shall I just use the armouring as the earth and ditch the third core or should I use both? So when would an install require a rod, on a TNC-S system?

 

[telectrix]

use both 3rd core and armour as cpc. then you still have cpc if steel rusts.. rod only needed if TNC-S and extraneous parts in garage, unless a 10mm bonding cable is added where the cpc is below that (allowing fot the steel as 8 times less conductive than copper ).

 

[buzzlightyear]

So when would an install require a rod, on a TNC-S system?

unless you have metal in there like pipes or oil drill,lol.

 

[GH Elec]

use both 3rd core and armour as cpc. then you still have cpc if steel rusts.. rod only needed if TNC-S and extraneous parts in garage, unless a 10mm bonding cable is added where the cpc is below that (allowing fot the steel as 8 times less conductive than copper ).

Right ok thanks a lot for your help telectrix. So if it’s a TNC-S a rod has to be used.
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your SWA needs protecting with a 40A fuse in the isolator. it does not require RCD; as long as you ensure the armour is earthed at supply end. the armour may be used as cpc for the garage sub. no rod needed.

I’ve just looked and the lowest fuse with it is 63A. Should I get a 40A fuse or will the 63 be fine

 

[telectrix]

Right ok thanks a lot for your help telectrix. So if it’s a TNC-S a rod has to be used.

not exactly. if extending TNC-S to an outbuilding with extraneous parts a 10mm bonding conductor is reqiured. the SWA may not be enough, so to save the expense of rumming in an extra boding cable, it's sometimes better to separate the earthing systems and TT the outbuilding.

 

[GH Elec]

not exactly. if extending TNC-S to an outbuilding with extraneous parts a 10mm bonding conductor is reqiured. the SWA may not be enough, so to save the expense of rumming in an extra boding cable, it's sometimes better to separate the earthing systems and TT the outbuilding.

Ok that’s good to know for future installs. Yh I can get hold of that pretty easy where I work.

 

[goasis]

I don't wish to be harsh, and I'll happily admit to having many gaps in my knowledge and experience, but I was wondering what area of electrical work you work in as you seem to have some slightly skewed ideas regarding OCPD's (or lack of) and RCD's providing additional protection.

 

[GH Elec]

I don't wish to be harsh, and I'll happily admit to having many gaps in my knowledge and experience, but I was wondering what area of electrical work you work in as you seem to have some slightly skewed ideas regarding OCPD's (or lack of) and RCD's providing additional protection.

I work on the Underground. Mostly done metal work conduit trunking tray ladder rack. Only recently out of my time. Believe it or not I have my inspection and testing qualification aswell. But just not done much of it that’s all.

 

[goasis]

I work on the Underground. Mostly done metal work conduit trunking tray ladder rack. Only recently out of my time. Believe it or not I have my inspection and testing qualification aswell. But just not done much of it that’s all.

Fair enough, I bet your tray and conduit work would put mine to shame then!! Maybe just a bit of brushing up on how and why we use fuses (over current devices) and RCD's needed then!! There's always more too learn, I feel pretty confident in some areas, much less so in others, esp compared too some on this forum!

 

[GH Elec]

Fair enough, I bet your tray and conduit work would put mine to shame then!! Maybe just a bit of brushing up on how and why we use fuses (over current devices) and RCD's needed then!! There's always more too learn, I feel pretty confident in some areas, much less so in others, esp compared too some on this forum!

Yeah it’s catch 22 though when it comes to things like this I’m not to hot on it where I’ve not done much of it. Yh I defiantly feel bit more confident about it now.

 

[Midwest]

There's the thorny issue of notification to the LBC; have you a solution to that?

 

[davesparks]

I work on the Underground. Mostly done metal work conduit trunking tray ladder rack. Only recently out of my time. Believe it or not I have my inspection and testing qualification aswell. But just not done much of it that’s all.

Presumably your training covered cable calculations for designing a circuit like this?

It's a sad reflection on the training you've been provided if they haven't managed to teach you this kind of thing in an apprenticeship.