Advise about getting power to a shed please

[Mike15979]

Hi

I'd like to put a shed in my garden but unless I can get power to it safely I'm not going to bother.
Rather than get an electrician around at this stage and potentially waste his time I thought id research it myself first.

I want a shed approx 5m from my property. I'm intending to use a max of 1500w at any one time.

The property is a garden/basement flat so running any new wiring back to the CU isn't an option.

The only way I could do it is from the existing ring main or would it be possible to use the existing cooker feed as it's not used any more.

Any advise greatly appreciated

 

[STEVEROG]

Firstly, I strongly recommend you get a competent spark.

If it were me (but I'm out of the game now so it's definately NOT going to be me)....

I would take a fresh feed from the incoming tails (henley block it as it is often referred). This new feed then supplies a totally separate small consumer unit which supplies ONLY the outside power. This is the most sensible approach. Note you could take feeds from exising rings but I personally think this is not best practice. You now want, as a bare minimum a 30mA RCD in the new small C-U. However, this means that if you trip the power while in the shed your in the dark AND you have to run back to house to reset the supply. The better option is to have a slightly higher and slower trip (apologies to sparkies for the simplifications) in the house and a 30 mA rcd in the shed. The idea here is that the shed RCD provides the anti-death device but the supply up to the RCD is still RCD protected, albiet a bit less stringent. Now run the correct sized SWA (armoured cable) to the out-building.

The above is a gross simplification. You need to do the calcs to determine the correct size cable for the run lenth. You also need to spec the overcurrent protection. If this isn't done correctly you may end up with an installation that doesnt meet the volt drop and disconnection time limits etc. The cables also need to be routed in the correct place, be terminated correctely etc. This is why this is a job for a full time professional installer.

Regarding re-using the existing cooker cable. The simple answer to this is that it is possible to do this BUT I would say that really this is only for the part of the run that is inside the property. This existing cable and the SWA would then need to be jointed properly. I wouldnt consider chokky blocks to be acceptable - soldered jointing with expoxy please! Better to fit a new cable all the way if you can.

I'm sure you can find a decent Spark on here who will give you a sensible quote?

Steve

 

[Mike15979]

Hi Steve

Thank you for taking the time to reply

When you say take a feed from the incoming tails, where do you mean by that?

Apologies, I'm not great with electrics.

I won't be doing the work myself I just need to know that it's possible without destroying my flat.

 

[Mike15979]

Or, as i plan on moving in the summer, could I use a extension lead as a temporary measure?

 

[ricicle]

. The better option is to have a slightly higher and slower trip (apologies to sparkies for the simplifications) in the house and a 30 mA rcd in the shed. The idea here is that the shed RCD provides the anti-death device but the supply up to the RCD is still RCD protected, albiet a bit less stringent. Now run the correct sized SWA (armoured cable) to the out-building.

Why do you need to RCD protect the armoured cable ? (assuming it is not a TT supply)

 

[JohnW2]

. The better option is to have a slightly higher and slower trip (apologies to sparkies for the simplifications) in the house and a 30 mA rcd in the shed. The idea here is that the shed RCD provides the anti-death device but the supply up to the RCD is still RCD protected, albiet a bit less stringent. Now run the correct sized SWA (armoured cable) to the out-building.

Why do you need to RCD protect the armoured cable ? (assuming it is not a TT supply)

Indeed - and, in any event, why not just have a standard 30mA RCD at the house end - that would provide the 'anti-death' functionality (one of those infamous 'misconceptions') and would also, for what it's worth, 'protect' the SWA.

I would also add that the solution suggested is probably not going to be of interest, given that the OP wrote:

The property is a garden/basement flat so running any new wiring back to the CU isn't an option.

Kind Regards, John

 

[STEVEROG]

Only suggested RCD protecting the armoured as we don't know that it's actually JUST going to be a single length of armoured all the way to the CU. Most likely it will be the existing cooker cable with a joint to armoured. If there really isn't any way to get a new full cable run in then I think there is then a good argument to include protection due to the section of non-armoured cable.

Without viewing the property we can't know if there really is no easy way to get a full cable run in without causing any major damage. Best to not assume one way or the other!

Extension lead is of course allowed, you can pretty much do what you want with extension leads, which in itself is a bit of a joke! That said, If your going to do this you need to use an RCD protected extension lead and only roll it out when needed. I think you may be suggesting running it out to the shed and leaving it - not a good idea.

Standard 30 mA RCD at CU in house is great but if you trip the power in the shed your stumbling around in the dark and then have to run back to the house to reset the trip (as I stated earlier). However, if your happy to live with this then no problem at all.

Regarding "splitting the supply". You power running to your consumer unit. Before this enters the unit you could divide the into two new paths, one going to the original consumer unit and a new one to a new unit that serves the out-building.

30mA misconception! well your right, its a can of worms and if you want to get technical its a function of many variables: skin resistance which itelf will vary from person to person and depends upon skin moisture levels etc contact point to conductor and ground point, condition of the heart etc etc. I guess the 30mA figure is maybe a sensible level at which a reasonable level of safety is provided whilst avoiding frequent nuisance tripping. Don't know, I didn't write the regs!

 

[JohnW2]

30mA misconception! well your right, its a can of worms and if you want to get technical its a function of many variables: skin resistance which itelf will vary from person to person and depends upon skin moisture levels etc contact point to conductor and ground point, condition of the heart etc etc. I guess the 30mA figure is maybe a sensible level at which a reasonable level of safety is provided whilst avoiding frequent nuisance tripping. Don't know, I didn't write the regs!

As you may know, it's one of the bees in my bonnet - particularly the common, and potentially dangerous, misconception (amongst some electricians, as well as the general public) that, say, a 30mA RCD will limit the current through a victim (connected between L&E) to 30mA. That would only be the case if the fault current rose gradually, which is very rarely the case. In most situations, the magnitude of the current (prior to disconnection) will simply be determined by Ohm's Law and, in the presence of low skin resistance etc., the current through the victim could be considerably greater than 30mA. All a (properly functioning) '30mA' will ensure is that IF the fault current is above 30mA (not matter how much greater than 30mA), the duration of current flow will be limited to a level which will often (but not always) prevent serious injury or death.

Kind Regards, John.

 

[ban-all-sheds]

I would take a fresh feed from the incoming tails (henley block it as it is often referred). This new feed then supplies a totally separate small consumer unit which supplies ONLY the outside power. This is the most sensible approach. Note you could take feeds from exising rings but I personally think this is not best practice. You now want, as a bare minimum a 30mA RCD in the new small C-U. However, this means that if you trip the power while in the shed your in the dark AND you have to run back to house to reset the supply. The better option is to have a slightly higher and slower trip (apologies to sparkies for the simplifications) in the house and a 30 mA rcd in the shed. The idea here is that the shed RCD provides the anti-death device but the supply up to the RCD is still RCD protected, albiet a bit less stringent. Now run the correct sized SWA (armoured cable) to the out-building.

That SWA doesn't need RCD protection, so rather than do it your way, have a switchfuse in the house instead of the CU, and a CU with RCBO for the sockets and non-RCD lighting in the shed.

 

[Mike15979]

I'm confused now.

I suspected that the extension lead idea was a bad one.

There is no way to get a wire to the CU without causing major destruction.

What are my other options?

 

[westie101]

I suspected that the extension lead idea was a bad one.

Nah you've just seen some thread drift!! As long as it is not permanently in place (e.g. use and put away, why not!) but get one with an RCD at the house end

 

[JohnW2]

I'm confused now.

I'm a bit confused, too. You said that you "want a shed approx 5m from my property", which implies that you don't yet have the shed, and also that you are planning on moving next summer. Are you really going to get a shed just for a few (mainly winter) months - and how often are you going to need power in it during the winter. If only occasionally, to use an extension lead (only 'when required') would probably be your simplest/best option for this short-term need.

Kind Regards, John.

 

[Mike15979]

Yeah I want a shed whether I move or not as I'll just let the place if I move and it really needs the storage space. I want power to it for 24/7 use, temporary would be ok but permanent would be ideal as I think itd pay for itself if I was to sell at any point

 

[westie101]

Ah, if you're looking at letting with a supply to the shed it would need to be permanent

 

[Mike15979]

Ah, if you're looking at letting with a supply to the shed it would need to be permanent

If I used a temp supply I would remove before I let.

I'm going off the temp idea really. Any ideas as a permanent solution?