Im i on the right track?

[padawan]

HI all

I have read these forums for while now, i have always enjoyed reading them, and found them very informative. Finally i get my chance to post a relevant thread. To start i should probably introduce myself a bit, i am currently training to be an electrician, and I'm working towards my NVQ.

So my boss is letting me design an installation and if all goes well it will help to complete a chunk of my NVQ. I have put a rough plan together so far, and was hoping to run it passed you guys, to see if i am going wrong anywhere, or see if there are any hints or tips i can pick up.

The job is running a new sub-main out to an outbuilding (garage in this case), and installing a distribution board, lighting circuit and ring/radial socket circuit. The supply to the property is a TNS system, 80 A supply, with a double pole isolator fitted.

My plan is run 3 core 6mm SWA for the garage supply, from the house consumer unit on a 40a MCB. In the garage install 40a DP RCD, 6a MCB for Lighting circuit, and either 32a/,20a/16a for socket circuit depending on ring or radial. I will run the socket circuit in PVC trunking, and the lighting circuit in PVC conduit. As the SWA will have to be run underground to the garage approximately 5 meters i will use corrugated plastic ducting. On the house side of the SWA i might have to use an adaptable box fixed the external wall, and run 6mm T&E to the consumer unit, as will there be a few 90 degree bends needed which could be problematic with the SWA.

I have a ew questions.

1. As the system is TNS supply, it is fine to export earth to garage supply?
2. On the house side of the SWA am i right that i should i use an MCB so that there is no RCD protection, reducing nuisance tripping? Or should i use a RCBO to make sure the SWA in also protected?
3. Is is best to use 3 core SWA and use 3rd core for earth?
4. I know SWA needs to be glanded both ends, but do both ends need to be bonded to earth? or just the house side?
5. Extraneous conductive parts. Are steel roof trusses an extraneous conductive part? The garage is concrete walls, on a concrete slab. So the trusses are structural steel, but not in contact with the ground, I'm not exactly sure where they stand as an extraneous conductive part.
6. If the trusses are extraneous conductive parts, then am i right that i should bond them in 10mm to the small garage consumer unit, or does it have to be run back to the main consumer unit in the house?
7. Is it best to run a ring or radial socket circuit in the garage? I would prefer 16a radial, but was thinking i might have to go 20a or 32a ring main, as the property owner will want to run a couple of freezers and washing machine etc, which could be an issue with max demand?
8. Does my plan sound ok, or would you suggest a different route? maybe henley block or something?

If you guys think i am on the right track then i will get back to you tomorrow about cable calcs etc. At the moment I'm thinking 6mm SWA, 10mm bonding, 2.5mm2 T&E for power circuit, and 1.5mm2 for lights (possibly singles as run in conduit)

Thanks for reading, sorry my first post was so long lol

 

[Richard Burns]

Welcome to the forum
1. You can extend the EPZ to the garage in general
2. SWA has earthed metallic covering and so does not need RCD protection
3. Probably the best solution
4. Both ends connected to earth
5. Probably not extraneous but probably worth testing just in case the concrete has metal reinforcement providing an earth path.
6. Main equipotential bonding goes back to the MET at origin.
7. For the loading at least a 20A radial, probably 32A ring may be better

 

[andyb]

As Richard says really except for a couple of observations.

2. This depends on how you run the 6mm t&e in the house, ie is it surface, in wall etc.
6. As it's a tns system you may get away with a 6mm bonding cable (if required) and use a core of the swa from the garage then just run a separate cable in the house.

You may have to run a separate earth in the house anyway as the 6mm only has a 2.5 cpc. you need to do an adiabatic equation to confirm.

 

[Simonslimline]

HI all

I have read these forums for while now, i have always enjoyed reading them, and found them very informative. Finally i get my chance to post a relevant thread. To start i should probably introduce myself a bit, i am currently training to be an electrician, and I'm working towards my NVQ.

So my boss is letting me design an installation and if all goes well it will help to complete a chunk of my NVQ. I have put a rough plan together so far, and was hoping to run it passed you guys, to see if i am going wrong anywhere, or see if there are any hints or tips i can pick up.

The job is running a new sub-main out to an outbuilding (garage in this case), and installing a distribution board, lighting circuit and ring/radial socket circuit. The supply to the property is a TNS system, 80 A supply, with a double pole isolator fitted.

My plan is run 3 core 6mm SWA for the garage supply, from the house consumer unit on a 40a MCB. In the garage install 40a DP RCD, 6a MCB for Lighting circuit, and either 32a/,20a/16a for socket circuit depending on ring or radial. I will run the socket circuit in PVC trunking, and the lighting circuit in PVC conduit. As the SWA will have to be run underground to the garage approximately 5 meters i will use corrugated plastic ducting. On the house side of the SWA i might have to use an adaptable box fixed the external wall, and run 6mm T&E to the consumer unit, as will there be a few 90 degree bends needed which could be problematic with the SWA.

I have a ew questions.

1. As the system is TNS supply, it is fine to export earth to garage supply?
2. On the house side of the SWA am i right that i should i use an MCB so that there is no RCD protection, reducing nuisance tripping? Or should i use a RCBO to make sure the SWA in also protected?
3. Is is best to use 3 core SWA and use 3rd core for earth?
4. I know SWA needs to be glanded both ends, but do both ends need to be bonded to earth? or just the house side?
5. Extraneous conductive parts. Are steel roof trusses an extraneous conductive part? The garage is concrete walls, on a concrete slab. So the trusses are structural steel, but not in contact with the ground, I'm not exactly sure where they stand as an extraneous conductive part.
6. If the trusses are extraneous conductive parts, then am i right that i should bond them in 10mm to the small garage consumer unit, or does it have to be run back to the main consumer unit in the house?
7. Is it best to run a ring or radial socket circuit in the garage? I would prefer 16a radial, but was thinking i might have to go 20a or 32a ring main, as the property owner will want to run a couple of freezers and washing machine etc, which could be an issue with max demand?
8. Does my plan sound ok, or would you suggest a different route? maybe henley block or something?

If you guys think i am on the right track then i will get back to you tomorrow about cable calcs etc. At the moment I'm thinking 6mm SWA, 10mm bonding, 2.5mm2 T&E for power circuit, and 1.5mm2 for lights (possibly singles as run in conduit)

Thanks for reading, sorry my first post was so long lol

You will need to carry out the appropriate test to confirm if the metal in question is an extraneous conductive part or not. Are you aware of how to do this?

 

[telectrix]

easy. wander lead. one end connected to L terminal, dab other end onto metalwork. if it goes bang, it's extraneous. :24:

 

[padawan]

HI guys thanks for your replies.

As Richard says really except for a couple of observations.

2. This depends on how you run the 6mm t&e in the house, ie is it surface, in wall etc.
6. As it's a tns system you may get away with a 6mm bonding cable (if required) and use a core of the swa from the garage then just run a separate cable in the house.

You may have to run a separate earth in the house anyway as the 6mm only has a 2.5 cpc. you need to do an adiabatic equation to confirm.

2. The 6mm T&E in the house will be run surface mounted, although i might run it in trunking for extra protection, i suppose i could even run it in singles especially if the CPC is only 2.5mm.
6. We have 10mm coming out of our ears, so to reduce cost/time i thought 10mm would be best, although it does raise a good debate lol

You will need to carry out the appropriate test to confirm if the metal in question is an extraneous conductive part or not. Are you aware of how to do this?

No I'm not, i have never done it before . Im assuming a continuity test though. How exactly would i go about it?

 

[markc123]

Can't add anything to whats been said.

However, why not a 4mm 32A radial ?