Extend new circuit from outhouse into another property with an existing supply, which is bad idea or not allowed?

Chris Pearson:

It's bad enough having sockets in the same room supplied from two (or more) circuits, but supplied from two different installations is asking for trouble as Graham has already said.


Why are the existing sockets not suitable?

What if I isolate the existing power supply for the power sockets and only leave power sockets from the new supply?

We could share the earth from the existing power supply (Building B) and use the power supply from Building A?


Existing sockets are part of a ring for the power sockets for the whole house which is shared by several appliances including a massive boiler.

Adding these extra appliances will far exceed the rating for the power supply and the building has concrete floors with tiles on them and brick walls with no insulation. It is also 3 rooms away from the consumer unit which makes it much more effort intensive to run a new circuit to it.

Is something I am doing here not allowed?

Can I just get electricity supply from the outhouse to Building B and extend and use the earth of sockets already in Building B?

gkenyon:

I'd be thinking more about safe isolation and maintenance - even in domestic premises, the designer has to think about whether it's safe for maintenance, repair and decommissioning activities under CDM (that duty applies regardless of whether the project is notifiable, and regardless of it being domestic premises). It's not only fixed-wiring electricians that will work on electrical equipment in the Utility/Laundry room, but appliance engineers. They would likely never consider someone derived the supply for the machines from a second source of supply!


Similarly, the users - if a machine starts smoking and they don't feel comfy unplugging, which "big red switch" do they turn things off at ?

I planned to install a big Red 40A isolation rotary switch at the incoming point marked "Emergency Socket Power Switch Off" and that would provide isolation to the power supply for the sockets.


They would also be protected by RCBO's (unsure if is an option if I want to share earth from the existing building and use power supply from outhouse) or an MBC + RCD.

AJJewsbury:

Is something I am doing here not allowed?

I don't think it's completely prohibited, but you're certainly skating on very thin ice.

 

Can I just get electricity supply from the outhouse to Building B and extend and use the earth of sockets already in Building B?

In principle yes, but there are some very significant practical problems. How would isolation of building B work if an earth fault (or just standing earth leakage) could energise building B's earthing system from building A's supply? How would you satisfy the requirement for c.p.c.s within cable to be earthed in the same installation as the associated protective device, or where an overcurrent device is used for fault protection that the protective conductor be incorporated into the same wiring system as the live conductors or their immediate proximity?


I'd advise a re-think. What's the current arrangement for supplying the dishwasher & washing machine? - there's likely to be a lot of diversity to be had there which might not be apparent. A while ago there was I think a wiring matters article about ring circuits that demonstrated the load from a typical kitchen appliances over some hours and how the 20A cable wasn't overloaded for long periods.


   - Andy.

Thanks for the inputs Andy, what risks exist if all of the power sockets in that room are powered by the power supply from the new building?

I will also provide a big red rotary isolator with clear labels to indicate its purpose to provide safety isolation; though I guess that doesnt talk about the earth standing earth leakage - how do I address that?


Existing sockets are part of a ring for the power sockets for the whole house which is shared by several appliances including a massive boiler.


Adding these extra appliances will far exceed the rating for the power supply and the building has concrete floors with tiles on them and brick walls with no insulation. It is also 3 rooms away from the consumer unit which makes it much more effort intensive to run a new circuit to it.


I have run an 8 week energy monitoring exercise to examine demand and can conclude I would have no way of running the additional appliances without a new circuit.


This is an old property which is a large house and to give you an idea of how insane the power usage is they use an approx. 30,000 kWh of power each year just from the detached house and garage.....

Existing sockets are part of a ring for the power sockets for the whole house which is shared by several appliances including a massive boiler. Adding these extra appliances will far exceed the rating for the power supply and the building has concrete floors with tiles on them and brick walls with no insulation. It is also 3 rooms away from the consumer unit which makes it much more effort intensive to run a new circuit to it.

FaeLLe:

Existing sockets are part of a ring for the power sockets for the whole house which is shared by several appliances including a massive boiler.


This is an old property which is a large house and to give you an idea of how insane the power usage is they use an approx. 30,000 kWh of power each year just from the detached house and garage.....

That consumption suggests an electric boiler, which probably ought to be on its own circuit. Can that not be arranged?

the power usage is they use an approx. 30,000 kWh of power each year

AJJewsbury:

Existing sockets are part of a ring for the power sockets for the whole house which is shared by several appliances including a massive boiler. Adding these extra appliances will far exceed the rating for the power supply and the building has concrete floors with tiles on them and brick walls with no insulation. It is also 3 rooms away from the consumer unit which makes it much more effort intensive to run a new circuit to it.

Presumably as gas or oil boiler - not fully electric? So the ring is only supply the pump & controls - so likely load probably less than an amp?


What sort of floor area are we talking about for the whole house? 30A rings were originally designed for 1000 ft² post-war houses with no thermal insulation with electric heating used simultaneously in two or three rooms.


Would it make sense to split the ring? E.g. a couple of new cables to some point on the existing ring (hopefully nearer the CU than the new appliance) back to the CU and turn the single ring into two?


   - Andy.

House is around 2000 sq ft and the garage is maybe just under 500 sq. ft. Solid brick walls with cavity insulation and large ventilation grills on the wall (that lets air pass through both interior and exterior wall as the property is in a Radon affected area).


The boiler is gas powered but fires up every time a tap or heater is turned on. The other appliances are several mixers, grinders, food processing units in a kitchen that operates pretty much all through the day, qutie a lot of datacenter kind of servers (each server pulls 3kw sometimes), networking equipment and what not.


Appliances coming in will be expected to used 3-4x a day (and each cycle runs upto 90 minutes) and due to housekeeping demands / shift patterns it is hard to predict when they will be used. The same devices (dishwasher and washing machine) also exist in another part of the house and could be used simultenously; they would share the ring if a new supply was not pulled in.


Really impossible to bring a new circuit in without a lot of civil works and they are already pushing the 60A home fuse limit! Since there is another 3 phase supply in the grounds they are keen to use that.