Power Supply

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 mypyrex 01 Jun 2020

In another thread I mentioned the existence of a 2.5 earth cable running across (underneath) our lawn from the garage. As far as I can see it comes straight from the consumer unit and supplies three twin power sockets. There does not appear to be a "return" to the consumer unit so does not appear to be a "ring".

Can anyone on here comment on the acceptability of such an arrangement?

Thanks

Post edited at 09:53
 henwardian 01 Jun 2020
In reply to mypyrex:

You mean there is a live, neutral and earth cable from the consumer unit and each goes from consumer unit to power point 1 to power point 2 to power point 3 and then terminates at power point 3?

Are you sure there isn't a connection from power point 3 back to power point 1? If there is, it still functions as a ring circuit without the extra expense and complexity of running an additional cable under the lawn (the "ring" would look more like a "p" shape in this case with the consumer unit at the bottom of the p). If there isn't then I'm not aware of any serious risks (assuming cables are thick enough for the load) but you might get a voltage drop on power point 3 if running things from power point 1 and power point 2, in practical terms I'm not convinced this would be enough to make a difference to your appliances though.

 Oceanrower 01 Jun 2020
In reply to mypyrex:

It might not be to code but hardly any different than running an extension lead.

OP mypyrex 01 Jun 2020
In reply to henwardian:

Thanks, I see what you mean.

 Ridge 01 Jun 2020
In reply to henwardian:

That would be my guess, simply  to save money on the SWA cable mentioned in myprex's last post. I suspect 99% of garages and sheds will just be a single spur as he describes, (without the return from socket 3 to 1). As long as he's just plugging in a radio or the occasional home power tool it shouldn't be an issue.

 Toerag 01 Jun 2020
In reply to mypyrex:

The benefit of a ring circuit is that it gives double the current handling ability of the circuit - twice as much cross-sectional area reduces the voltage drop and heating effect. It also gives fault tolerance in the event of disconnection damage to one leg of the ring (but conversely increases danger as you now have two live ends).

What you're likely to have is a 'spur' off your consumer unit to your shed, then either a daisychain of sockets / lights off that spur, or a ring(s) of sockets/lights within the shed off the spur to it.  The 'safe' way to do the shed would be to have the incoming spur cable from the house going into a 'daughter' consumer unit from which you run separate lighting and power circuits within the shed.  This allows you to fuse the lighting circuit and power circuits appropriately, and keep the lights working in the event that the power circuit goes faulty - you don't want to be using a power tool in the shed of a winter's evening and have it trip out the lights.  Unless a ring is needed to the shed for some crazy reason, its cheaper and easier to use a spur to the shed. 

Someone will no doubt be able to tell you the safe working load / volt drop of your spur if you tell us how long the cable run is and the thickness of the conductors.

Post edited at 11:23
 jkarran 01 Jun 2020
In reply to mypyrex:

Doesn't sound like it's strictly by the book. What's the breaker rating? I'd check it's not routed through any thermal insulation inside the house but in general I'd think it's safe enough for light duty use in a shed. 

Jk

 Ben Bowering 01 Jun 2020
In reply to mypyrex:

A single feeder that doesn't include the return leg to the consumer unit required to make it into a ring circuit is known as a radial circuit (it is not a spur, which is a radial subcircuit off a ring or another radial circuit). Radial circuits are perfectly acceptable under bs7671. 

However, a 2.5mm t&e radial circuit supplying sockets must be protected by a 20A (or lower) rcbo and since it is buried it must be enclosed in a suitable conduit or duct, and be at a sufficient depth to avoid being damaged by any reasonably foreseeable disturbance of the ground, and be marked by cable covers or marker tape.

It sounds like a DIY bodge and the earthing and bonding requirements are quite likely to be inadequate. More info is needed to determine exactly what the requirements are, such as supply arrangements (e.g. pme, tt etc.), presence of extraneous conductors, exposed conductive parts, garage construction etc..

 marsbar 01 Jun 2020
In reply to mypyrex:

I think you should consider getting a qualified electrician to have a look at it.  

 Ben Bowering 01 Jun 2020
In reply to mypyrex:

Edit to my previous post: compliance with bs7671 is not a legal requirement so long as you don't let the property or misrepresent compliance to your insurers or future buyers. So long as you don't disturb the cable and either: establish the earthing and bonding is adequate, or: make sure there are no exposed conductive parts (i.e. the sockets are plastic with plastic screw caps and you only use double insulated appliances) then continued use is probably low risk. Usual caveats apply. 


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