sorry but...

[Apache]

Right...It's one of those newly built houses made of matchsticks! CU in a c/b off the hallway with the kitchen/utility area behind it. The owners have only lived there for 2 weeks, so don't really want all their pretty decor ruined, so the only option is to spur from the d/s ring.

They have a Legrand CU with a 100A main fuse - only 5 circuits plus 2 lighting circuits which are RCD protected. Wasn't able to do any more checks as it was pitch black (even the torch wasn't helping!) and getting late - so I told them I'd have to return to do further checks.

With such little info at this stage, am I able to give a rough cost estimate as I think the price of the job will determine whether or not they go ahead at the end of the day?

what kind of earth?

 

[avinalarf]

Hi Apache

I'm afraid to say I didn't even get to check that - several kids running around - lots happening in the house, which is why I said I'd return at the weekend.

Whilst on the subject of earthing - when/why are certain types of earthing arrangements used ie: why would a house have TN-S instead of TN-C-S? Does it have anything to do with when the property was built?

 

[springcrocus]

Evening, Nat, may I suggest the following?

Because you are in the early days of your chosen career, it is important for you to build up a client database. Occaisionally, you will underprice yourself BUT if you end up with a satisfied customer, you may well get work from the people that the customer recommends you to. Compensation for the loss of earnings on this job!

With this in mind, assume a straightforward job (it probably won't be, but never mind) and give a price based on how you would do it in your own home and how long you think it would take (half-day, whole day) plus materials.

Don't be too pricey on materials. If you need ten metres of 6mm SWA, buy a fifty metre roll and charge for a fair proportion of the roll - you will use the rest on another job another day. This will keep your price down a bit.

Post #6 by Specs would help you regarding the "how".

I always look at a job (not neccessarily electrical installation, I mean any job) from the "is it worth doing?" point-of-view. If I wanted this done at home, is the cost worth it? Will your customer think they have got value-for-money?

Don't be frightened to tell the customer it would not be cost-effective if this is what you really feel. The respect you gain from them for your honesty is worth a stack of new work in the future from their friends and relatives (been there, done that, still here).

The only final advice I could offer is, go for it and, if they say OK, then keep a really good check on how long it takes you - itemise it; drilling the holes, laying ther cable, joining it up, testing it, etc - and use this info to help you get the price right on the next job. Better to be a bit too cheap now and get repeat work than to be too pricey and get no further work.

I think I need more wine, I'm starting to sound like my Grandma Blushing

 

[avinalarf]

SpringC - have another wine Applaud Smiley - you deserve it. Advice from all contributors has been greatly appreciated. Thanks for the note about the swa 'cos I was just looking at pricing for 10m!

Slips, I told them about considering whether the freezer was ok to be kept in a shed - they're going to check the manual (once they find it!) ?:| .

I did say to the customer, that it was quite a bit of work just for a small chest freezer in a shed that's so close to the house. She began talking of buying a different one before I'd even left, so I doubt that they're going to go ahead anyway .

 

[avinalarf]

No prob's then! Re the exporting earth bit ...

best to read the article..

"Electrical installations outdoors: a supply to a detached outbuilding (243 k)"

(or print a copy to keep for future reference)

which can be found here..

Wiring Matters magazine - 2005 issues - The IET

it should answer all of your questions..

if not come back after reading it?

SL

SL - have read the above article which was very helpful. I do have a question though and I hope it doesn't make me appear too dumb!

If one was to use the "spur off main ring" method, why would the DP switch be required in the garage before the so? Is it just for maintenance purposes of the so or fused spur above it?

Also, would the only way to provide RCD protection be via an RCD socket?

SpringC mentioned plastic fittings being essential if using PME - I gather this would be the case here then?

There are no extraneous fittings in the shed - they literally had it built last week, purely for storage purposes.

 

[Apache]

SL - have read the above article which was very helpful. I do have a question though and I hope it doesn't make me appear too dumb! If one was to use the "spur off main ring" method, why would the DP switch be required in the garage before the so? Is it just for maintenance purposes of the so or fused spur above it?

Single means of isolation for the shed?

Also, would the only way to provide RCD protection be via an RCD socket?

RCD Fused spur? MCBO on whole ringmain? Is there RCD protection on the circuit?

SpringC mentioned plastic fittings being essential if using PME - I gather this would be the case here then?

why not? not exactly an industrial workshop and with your DP switch you can afely isolate the shed to change the broken fitting

There are no extraneous fittings in the shed - they literally had it built last week, purely for storage purposes.

Thought I'd have a go at replying

Wish I had a bigger shed............

 

[SPECIAL LOCATION]

SL - have read the above article which was very helpful. I do have a question though and I hope it doesn't make me appear too dumb! If one was to use the "spur off main ring" method, why would the DP switch be required in the garage before the so? Is it just for maintenance purposes of the so or fused spur above it?

IMHO, DP switch to provide local isolation so any maintenance work on the electrics in the shed can be done without the risk of someone switching the FCU back on in the house.

Unless of course you are going to lock off the whole of the ring circuit at the CU MCB?

Also' date=' would the only way to provide RCD protection be via an RCD socket?

[/quote']

RCD FCU at connection in house?

or if house Ring is already RCD protected.. which it probably should have been anyway.. (16th sockets likely to supply outdoor appliances?) the house RCD will do the job. and it will already be 30ma

Preferably I would put shed back to own circuit at CU with own RCD or RCBO

so it don't inconvenience house ring if rats go chewing the shed!

SpringC mentioned plastic fittings being essential if using PME - I gather this would be the case here then?

? ?:| :| I cant say I would agree with that statement?

Any metal fitting appropriately earthed in accordance with correct disconnection times ZS limits AND with additional RCD protection is as safe as a nice polished chrome metal fitting inside the kitchen on a PME installation...

or any Non class II item or equipment for that matter.

Personally I would use metal clad fittings in garages sheds workshops and the like' date=' far more robust..

If you had several sockets and want to join your bits up with SWA you have a nice sturdy structure to connect onto.

its not uncommon for sheds workshops etc.. to have uneven walls or movement in the walls, which can crack plastic back boxes. breaking the fixing holes to the wall.

I have replace too many plastic shed / garage fittings for me to consider them worth while in that environment.

Metal fittings appropriately earthed.

If the shed is ALL wood, no earthy extraneous metal parts, close to house.

NO parallel earth paths introduced, Volt drops, ZS's and disconnection times all compliant....

Then Exporting the house earth to the shed is no more dangerous than Joe public taking their 25m B&Q extension reel out into the garden from a plug in the house.

or working from the attached garage with a lead out onto the front drive vacuuming the car!

There are no extraneous fittings in the shed - they literally had it built last week, purely for storage purposes.

extra note re slipshods point fridge & cold weather,,,

When a freezer refrigerant gas goes from high pressure to low pressure, the temperature of the gas drops. a freezer is circulating a gas from high pressure to low pressure over and over again. there is a compressor and a closed tube of refrigerant.

The compressor pumps the refrigerant and compresses it. The refrigerant flows through the coils on the back of the freezer and through an expansion valve to the inside of the freezer. As the refrigerant passes through the expansion valve the pressure drops and so does the temperature.

The cold low pressure refrigerant warms up from the stuff inside the freezer absorbing heat from the freezer. Because this relies on warmer temperatures outside the appliance for the process to work. If the temperature outside a refrigerator or freezer, is too low, the appliance will not cool efficiently and the freezer will probably be too warm.

 

[springcrocus]

? ?:| :| I cant say I would agree with that statement?

Any metal fitting appropriately earthed in accordance with correct disconnection times ZS limits AND with additional RCD protection is as safe as a nice polished chrome metal fitting inside the kitchen on a PME installation...

or any Non class II item or equipment for that matter.

Yes, definitely a bit over the top.

However, I was answering Nat's question about the dangers of PME and just using it as an example of what could go wrong. The more graphic or extreme an example, the easier it is to grasp the principles.

I remember a science lesson in school a couple of centuries ago. The teacher was going to tell us all about boilers. His opening statement was "The first thing to know about boilers is that they explode".

From that moment on he had us hooked.

 

[avinalarf]

IMHO, DP switch to provide local isolation so any maintenance work on the electrics in the shed can be done without the risk of someone switching the FCU back on in the house.Unless of course you are going to lock off the whole of the ring circuit at the CU MCB?

OK!

RCD FCU at connection in house?or if house Ring is already RCD protected.. which it probably should have been anyway.. (16th sockets likely to supply outdoor appliances?) the house RCD will do the job. and it will already be 30ma

Preferably I would put shed back to own circuit at CU with own RCD or RCBO

so it don't inconvenience house ring if rats go chewing the shed!

Ring to be broken into is already RCD protected, so RCD FCU not required. Can't remember if I'd mentioned previously, but to take shed circuit back to CU would be much more remedial work for client, so not really an option in this case.

? ?:| :| I cant say I would agree with that statement? (re: only plastic fittings in shed)Any metal fitting appropriately earthed in accordance with correct disconnection times ZS limits AND with additional RCD protection is as safe as a nice polished chrome metal fitting inside the kitchen on a PME installation...

This is what I thought, but wasn't 100% sure.

Personally I would use metal clad fittings in garages sheds workshops and the like, far more robust..If you had several sockets and want to join your bits up with SWA you have a nice sturdy structure to connect onto.

Metal fittings appropriately earthed.

Right, this is where I'm getting a bit confused... :_| Obviously I'll use swa as the cable will be running outside. BUT, regarding what SpringC said (and Steps, I think) - how do I terminate the swa sheath?

This is what think I can/should do:

Use 2-core 6mm swa (according to calcs, I could use 4mm, but thought better to use 6mm) and banjo the earth sheath at both the FCU end in the house and the DP switch in the shed. Run all cables after the DP switch in conduit if not using swa. Would 3-core be better? If so, why?

Someone please correct me if I'm wrong.

If the shed is ALL wood, no earthy extraneous metal parts, close to house.NO parallel earth paths introduced, Volt drops, ZS's and disconnection times all compliant....

Then Exporting the house earth to the shed is no more dangerous than Joe public taking their 25m B&Q extension reel out into the garden from a plug in the house.

or working from the attached garage with a lead out onto the front drive vacuuming the car!

So why the ABSOLUTE "NO,NO" about exporting PME then? Does it just become an issue if there are extraneous paths in the outbuilding?

extra note re slipshods point fridge & cold weather,,,When a freezer refrigerant gas goes from high pressure to low pressure, the temperature of the gas drops. a freezer is circulating a gas from high pressure to low pressure over and over again. there is a compressor and a closed tube of refrigerant.

The compressor pumps the refrigerant and compresses it. The refrigerant flows through the coils on the back of the freezer and through an expansion valve to the inside of the freezer. As the refrigerant passes through the expansion valve the pressure drops and so does the temperature.

The cold low pressure refrigerant warms up from the stuff inside the freezer absorbing heat from the freezer. Because this relies on warmer temperatures outside the appliance for the process to work. If the temperature outside a refrigerator or freezer, is too low, the appliance will not cool efficiently and the freezer will probably be too warm.

Wow! That was a good lesson on how freezers work.

I can't thank everyone enough for their input. I do feel like I'm being a pain at times, but I'd rather run the risk of looking stupid, than endangering mine or someone else's life!

Nat

 

[SPECIAL LOCATION]

Yes, definitely a bit over the top. ......

.....

The more graphic or extreme an example, the easier it is to grasp the principles.

Applaud Smiley:x

As long as you ain't going to say you run your lights in 6.0mm

in case the cable melts cuz you put a 500w halogen bulb in the circuit !!! :^O :^O:^O:^O:^O;\ ]

 

[SLIPSHOD & SLAPDASH]

Go down to B&Q and buy an extension lead, throw this out of window and plug in freezer. hey presto, job done