Well if the DNO want to remove the unused supply (if the OP decides to use only one supply) then they have every right to do so. But they have to pay for it's removal and not the OP.
Depending on how the OPs incoming supply is done that could mean digging up pavements or worse still digging up roads.
Two words
Russ Andrews
In message , ARW writes
Incoming supply is overhead, which makes life easier.
Thanks for all the comments - very useful. It seems that the whole job could make economic sense. I like the idea of just running one fat cable from the house CU through to the shop, and powering everything from that. The shop usage is fairly minimal, just power sockets, alarm and lighting, ie no showers, cookers etc.
Disruption should be minimal. Take the cable from a spare outlet on the house CU and, at the shop end, remove the tails from the meter to the CU, and connect the cable to the CU. No need to remove the shop end CU, switches etc.
Switching the shop to supply to a no cost option (remove it or no standing charge tarrif with zero use) gives you £245/year, less cost of 1500 units on the house supply, perhaps £100/year. guesstimate £400 to get the work done, 4 years...
Snag with that is if you turn off the house supply for any reason the shop goes off as well. Split the tails, fit the required switch fuse into the sub-main to the shop CU and the shop can be on with the house off or vice versa.
Even better! Yes, cutting the power to the shop always sends the alarm into a tizzy, so best avoided if possible. It is an ex Post Office, so fully alarmed even though no longer in service.
Power cuts setting off alarms are often cured by replacing the battery in the alarm control box.
It's not much of a snag is it?
How often does the average householder have to turn the house supply off?
I know it's not much load, 1500 unit pa.
Poor assumption, it could be a 16 kW load for 30 mins every other day:
16 * 0.5 * (365 / 2) = 1460 kWhr.The 24/7 load is a mere 170 W (0.17 * 24 * 365 = 1489 kWHr).
In reality the peak load will be somewhere between the two, maybe 4 kW for a kettle plus a 1 kW of other load but remember *everything* is going through that single MCB in the house CU, so you loose diversity. Overload the house CU MCB and everything goes off in the shop. Overload an MCB in the shop CU fed with a sub-main only that MCB goes off, perhaps the lights stay on...
Not mention that having a seperate supply available when the other is off for some reason is handy.
It depends. If you have say a 32A & 6A shop circuit fed from a >38A MCB then you're unlikely to trip both circuits if one trips.
NT
It's not a poor assumption. The OP has already said that there are no high load circuits such as cookers or showers in the (ex) shop. He has also suggested that the shops sockets power could be integrated into the house circuit by extending the house circuit ring to incorporate the shop ring and similar for the lights.
Supplying everything through one MCB or fuse is a good example of how diversity is applied and is not a loss of diversity.
Not if it's a fault current:-)
The battery is fine. The alarm does not go off, but the control box emits constant warning beeps, and requires resetting.
In message , ARW writes
Quite right. I don't use anything high powered in there, not even a kettle. However, I am aware that, should the house be sold at any time, a new owner may behave differently, so both power and lighting circuits must be up to normal spec. Having said that, if anyone in the future converted it to, say, a granny flat, it is not unreasonable to assume they would check carefully and install new runs if installing, say, a power shower.
The graphs at
NT
I think he meant discrimination.
not all fault currents have looked at the graph though ;-)
In most cases discrimination will be maintained. The fact that ocasionally it isn't is rather trivial, and hardly worth a protracted discussion. The op knows the options.
NT
How on earth can you say "in most cases discrimination will be maintained" from those graphs and keep a straight face?
In many cases of *overload*, discrimination will be maintained - at least with a single downstream MCB one rating step or more lower than upstream.
With multiple MCBs downstream (say a CU on a submain) its probably still likely - but somewhat less so.
However with a 500A fault current why would you expect the magnetic response of the lower trip current device to be necessarily faster than that of the higher rating device?
(its for this reason one often elects to use a HRC fuse for the head end of a submain)
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