Garage Wiring - Socket Lighting Advice

[SimonH2]

... do the work myself (ie the cables, boxes etc) and then get a qualified sparky in to give it the once over and hopefully all beign well connect it up and sign it off.

The law does not allow for that.

The ONLY options are :
a) The sparky does the work and notifies through his approved body - note that he is required to sign a form stating that he designed and installed the system.
b) You notify your local authority building control dept, pay their fees, do the work, tell them you;ve done - and they provide a certificate. You may also have to either pay a sparky to do test, or pay extra for LABC to do tests, before they'll sign it off.

However, I think this does not need notification. The circuit already exists (albeit having been temporarily disconnected while the water ingress was sorted) - so all you are doing is altering an existing circuit. You still need to comply with "Part P" which effectively means complying with BS7671 (aka "the wiring regs).

 

[lozinger99]

Hi all, Cheers for this.

So, after all the advice, many thanks, I a had a sparky round to have a look and he said the existing cable was 1.5mm and I need a 6 mm (?) - anyway he said the existing cable would not support three sockets and the lighting so Id need a new one.

Which means getting one ran down to the house (through extension roof down into hallway - he said 600 mm trench (to be dug out by me), all the work, fitting cable, three sockets, four lamps in garage. Just north of £800.

Bit more than (my wife ) will let me sign off on this project.

Probelm also Is digging that trench out, will destroy the garden now - does it have to be underground?

 

[JohnW2]

So, after all the advice, many thanks, I a had a sparky round to have a look and he said the existing cable was 1.5mm and I need a 6 mm (?) - anyway he said the existing cable would not support three sockets and the lighting so Id need a new one.

That's a bit of a sweeping generalisation - it all depends upon the load. If your total requirement is for less than about 18A, then, by my reckoning, ~13m of 1.5mm² SWA ought to be OK.

Kind Regards, John

 

[lozinger99]

Hi John,

Thanks.

I think on a max day - Id be using a TV, a DVD player, a fridge, a freezer and lighting simultaneously.

Forgive my ignorance re the output of that, but Im guessing thats quite a lot?

 

[ban-all-sheds]

Hi all, Cheers for this.

So, after all the advice, many thanks, I a had a sparky round to have a look and he said the existing cable was 1.5mm and I need a 6 mm (?)

6mm² That's a big jump - what are you going to be using the workshop for?

That said, the difference in price for 6mm² compared to a smaller size would be pretty insignificant, so if you are going to replace it you might as well put a larger size in, then you would have capacity if you decide to take up pottery or glassblowing or sub-atomic physics.

anyway he said the existing cable would not support three sockets and the lighting so Id need a new one.

What are you planning to use the sockets for? Did he ask? Did you tell him?

1.5mm² cable will carry a tad over 18A for that distance. Actually from the cable's perspective, 20A would be fine, but technically it would not comply because voltage drop would be too high for a circuit with lighting on.

What rating is the breaker supplying the garage? Does the electrician propose to change it? Did he recommend 6mm² for future-proofing?

Which means getting one ran down to the house (through extension roof down into hallway - he said 600 mm trench (to be dug out by me), all the work, fitting cable, three sockets, four lamps in garage. Just north of £800.

Bit more than (my wife ) will let me sign off on this project.

She might be right. That sounds too high. Is the route through the house very tricky? I wonder if he doesn't actually want the job.....

Probelm also Is digging that trench out, will destroy the garden now - does it have to be underground?

Probably - it's not easy to safely get cables from a house to a garden building any other way. Unless overhead on a support wire is an option?

 

[ban-all-sheds]

I think on a max day - Id be using a TV, a DVD player, a fridge, a freezer and lighting simultaneously.

I thought you said workshop?

Is this why SWMBO is objecting?

Forgive my ignorance re the output of that, but Im guessing thats quite a lot?

Nowhere near the limit of a 1.5mm² cable on a 20A breaker.

 

[JohnW2]

I think on a max day - Id be using a TV, a DVD player, a fridge, a freezer and lighting simultaneously. Forgive my ignorance re the output of that, but Im guessing thats quite a lot?

That's really not very much at all - nothing like the 18A I mentioned - it's only really if you get into heaters/dryers etc. (or large power tools) that loads start getting high.

How cold does it get in your garage in bad winters? I only ask because, rather ironically, a good few fridges and freezers seem to stop working if the ambient temperature gets below 'zero' (°C).

Kind Regards, John

 

[lozinger99]

Hi Guys

I thought you said workshop? icon_cool.gif

Well, workshop/pub. Mostly pub.

She might be right. That sounds too high. Is the route through the house very tricky? I wonder if he doesn't actually want the job.....

No the route is pretty straightforward, even to the eyes of a DIY newb like myself. I think he was honest, but maybe just the sort of guy that would put skyscraper footings into a shed base, which I respect in one sense, but for me, (and for cost purposes) enough is good enough. And perhaps your right re wanting it.

That's really not very much at all - nothing like the 18A I mentioned - it's only really if you get into heaters/dryers etc. (or large power tools) that loads start getting high.

How cold does it get in your garage in bad winters? I only ask because, rather ironically, a good few fridges and freezers seem to stop working if the ambient temperature gets below 'zero' (°C).

just the regular British winter. Chances are id not be using it, depths of winter anyway.

Ok so you think a few appliances mentioned might be OK off the existing.. perhaps ill get another guy in to have a look.

 

[JohnW2]

just the regular British winter. Chances are id not be using it, depths of winter anyway.

Fair enough, so long as the freezer is empty at the time!

Ok so you think a few appliances mentioned might be OK off the existing.. perhaps ill get another guy in to have a look.

I'm sure it would be OK with just the loads you have mentioned. If you don't envisage ever needing a lot more than that, why not get in touch with the original guy first, pointing that out to him and telling him that you understand that 1.5mm² SWA ought to be fine for that (with a suitable sized breaker - probably 20A in practice, but it could be 16A).

Kind Regards, John

 

[ban-all-sheds]

How cold does it get in your garage in bad winters? I only ask because, rather ironically, a good few fridges and freezers seem to stop working if the ambient temperature gets below 'zero' (°C).

You would only find that ironic if you didn't know how they worked.

 

[JohnW2]

How cold does it get in your garage in bad winters? I only ask because, rather ironically, a good few fridges and freezers seem to stop working if the ambient temperature gets below 'zero' (°C).

You would only find that ironic if you didn't know how they worked.

You're obviously having another quiet/boring day!

What you say is true - but since most people don't know how they work, most people probably do find it rather ironic!

Do I take it that fridges and freezers which can function with low ambient temperatures actually exist (and, if so, how do they work?)? I recently had to get a new fridge, and of the dozens whose specs I looked at, every single one indicated that the appliance was 'not suitable for use in outhouses', or words to that effect.

Kind Regards, John

 

[ban-all-sheds]

There are ones which work at lower ambient temperatures than the norm, but I don't know how low they go, or how the evaporator differs, or even if they work differently. Beko, for example, are very secretive about how their 'Freezer Guard' system works.

 

[SimonH2]

I suspect that most fridges & freezers use an orifice/capillary to modulate refrigerant flow into the evaporator. If ambient temperature is too low, the condenser pressure (the high pressure, HP, side of the system) will be low - and so low pressure differential across the metering orifice (EDIT) leading to low refrigerant flow rate and limited cooling.
In theory, this could be compensated for by lowering the pressure in the evaporator (in the LP side of the system) - but there is a practical lower limit.

I suspect most systems also have high & low pressure switches - so won't work if there is little/no pressure in the HP side. Usually the HP switch is there to stop the compressor when pressure is too high (typically unable to lose heat from the condenser). The LP switch is often there to inhibit the system if it's lost it's refrigerant.

One very simple way of making the system work at lower ambient is to change refrigerant. Many outdoor types will be familiar with the problem of butane stoves not working at low temperatures (around freezing) and having to switch to propane (or a propane/butane mix). I terms of refrigerant properties, propane is near identical to the long outlawed R22 (used to be near enough standard for industrial systems), while a 50:50 mix of propane and butane is equivalent to the old R12 (standard fill in automotive systems).

Of course, there are downsides of switching to a "lower temperature" refrigerant. Firstly, at any given set of temperatures, the pressures will be higher which means higher pressure components (= higher cost).
Secondly, the evaporating temperature may well be a lot lower - so instead of the refrigerant passing through the evaporator coil and progressively boiling off at a "reasonable" temperature, it may flash boil and chill part of the coil to a very low temperature. While in a freezer any condensate will freeze on the coil, this "shouldn't" be the case in a fridge most of the time. So using a lower temperature refrigerant may make condensate management more "interesting".
I suspect that efficiency could also be affected - though just the cost of "high pressure" is probably enough to stop most available units using refrigerants suitable for low temperatures.

 

[ban-all-sheds]

Not sure I'd want to boil propane or butane in an outbuilding anywhere near my house.

 

[SimonH2]

HC refrigerants were standard before someone came along and introduced ozone zapping CFCs. They are in a completely sealed system, and the quantities are very small - I believe typical charge quantities are in the order of 100g or less.
In the grand scheme of things, not a major risk. Consider you've (probably) got a piped supply of explosive vapour which you mix with air in a box* in the house and set fire to it. Good chance that you release some of it into the room** and ignite it. Not to mention the pressurised pipes carrying water hot enough to cause serious injury. Or the effectively unlimited supply of lethal voltage electricity.

* Boiler
** Gas hob or oven