I have a 3 phase supply of which only one phase is in use (used to have storage rads years ago). I want to install some underfloor heating and power to a hottub which needs another 70A of power which looks to be more than my present consumer unit can take. I was planning to install another consumer unit on one of the other phases. Are there any problems to look out for or drawbacks?
Does the system still have a 3 phase meter attached? If you're only using a single phase at the moment you're electricity bill will show this on the standing (equipment rental) charges. To use another phase, you'll need a proper meter to get the invoicing correct for the extra power you're going to use.
If you're being charged for 3 phase already, then you might as well change the whole distribution board back to 3 phase as well. That way you can use all phases to hearts desire.
Have a look for "Hager.co.uk" to see the pricing of the proper gear to get you going.
Yes, I have a 3 phase meter with tails to a MEM switchbox which used to be connected to a 3 phase coldstore compressor, now removed. I was simply going to take a supply from one of the unused phases via another consumer unit, which is in fact the way the present consumer unit is wired.
regarding the meter and supply, I am on a standard domestic tariff, and the bills make no mention of renting any equipment, simply a standing charge of
10.81p/day. The meter is just a bigger version of any other but with more wires coming out the bottom!
If all phases are still energised then you could do what you want with no problem, and from what you say in your other post you're being charged for the rental of a 3 phase system if it is being charged at £10.81 per DAY. A normal domestic meter rental charge is around £10.81 per Month.
It would be easier and neater, if all phases are still powered, to obtain a proper 3 phase consumer unit. This will let you balance the power you use across all phases at once. This stops your meter surging when you load only one phase with heavy loads and drop loads for lite appliances on the others.
Just my thoughts on this.
He said 10.81p, not £10.81.
Thanks for that. I only noticed my mistake after reading the post again when I'd sent it, by then it was to late to change it. Thanks again for pointing it out though.
The main problem is the added danger of the higher voltage.
Maintain a minimum of 2 metres between single phase outlets on different phases. For a house, it is probably easiest to keep each room on the same phase for everything, including lighting.
Any junction box, wall switch or other similar item that appears to be single phase must have a 415v warning sticker on it if you have more than one phase in it.
Colin Bignell
However, this shouldn't be a problem for a few fixed appliances such as the hot tub, unless there are controls shared with circuits off the main CU, such as a grid switch containing switches for the lights (off the original CU) and the heater/pump (off the new CU) etc.
Christian.
I don't think the standing charge for a 3 phase supply is really just under
4000 quid a year, either!Christian.
There should still be warning signs about there being more than one phase in use, what happens if someone runs an extension lead from one phase to work near on the equipment using the other phase, also there is the possible danger of the wrong CU feed being isolated etc.
It might not be strictly needed but in most domestic situation houses don't use more than one phase IYSWIM...
True, but £394 is more likely. So, I made a mistake, what of it? We learn through mistakes, don't we? Stop picking on me. I'm human. LOL :-))
That's why I would advise changing the whole CU to a single 3 phase unit, so no mistake can be made about which one to switch off.
But then other factors start to become an issue, like sharing the circuits of the house across the three phases of a 3ph CU. If there was really a concern about the wrong CY being isolated then perhaps un switched CU's should be used on both supplies with the main 3ph switch being the only means of isolation - either the whole building is isolated electrically or it isn't.
I would totally agree. However, segregation doesn't seem to be mentioned in the 16th edition.
Or did I miss it somewhere? :-)
The main reason for the notice is to ensure that someone taking the cover off is aware of the higher voltage being present. A three phase appliance supply should be obvious as soon as you expose the terminals, but it will not always be obvious if something that is normally used on single phase contains more than one phase. I use phase colours on the live wires, which makes it more obvious, as well as making circuits easier to trace, but I still use stickers. One such situation is the lighting in my factories, which is distributed across the phases and controlled from a central gridswitch, which carries all three phases.
Colin Bignell
I cite it as an avoidable H&S risk.
Colin Bignell
No, it's not there. I have a vague recollection there was something in the 14th edition regs, but I long since lost my copy, sadly.
Indeed the 2m seperation between phases is no longer a requirement. Something I know from my work in theatre lighting where maintaining this while loadbalancing was near on impossible.
Jeff - we seem to be in the same boat. We have a three-phase supply fused at a mere 63A per phase (although the meters are rated at only
40A!). Two of the phases are variously used for "backstage", domestic (including the caretaker's flat) and our "studio theatre"; the third phase is used for the dimmer packs and a few lights in the workshop/props store.Fairly recently we upgraded the dimmer packs to 36 x 10A channels - allowing for a bit of overhead the drain on the blue channel would be of the order of 400A (if every channel was fully laden!)
I would prefer to keep the dimmer pack to a single phase for segregation reasons.
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