Is it possible to tell if I have a 3 phase supply? Ask questions and find answers to many subjects relating to electrics and electrical work

[GC1955]

Hello. I have recently bought a house that needs doing up. A heating engineer came the other day and said when he looked at the consumer unit etc (which all needs replacing) that I had a 3 phase supply. I think he based that on the fact that there is a 100A fuse. There is however only one fuse. Could he be right? Could it be a 3 phase supply where one phase only is being used? I am sorry if this is a daft question. Here are a couple of photos. The yellow label on the side of the fuse says 1988. Most of this equipment has been there for donkeys years. Thank you in advance.

[Mr White]

You only have a single phase supply. I am curious as to why you said

I think he based that on the fact that there is a 100A fuse.

To have a fuse holder marked as 100A is normal, but it doesn't mean to say it has a 100A fuse inside.

[ericmark]

Not 3 phase, but some thing odd, as the henley blocks have a label saying it is an offence to interfere with this equipment so would seem these are before the electric meter, so maybe you have a looped supply?

Normally looped before the fuse, which means the fuse only supplies one electric meter, but if looped after the fuse swapping the consumer unit will likely mean step one is to have an isolator installed.

Swapping a consumer unit is a complex thing as in theory the DNO should remove the fuse the electrician should fit new consumer unit, then the DNO replaces the fuse. In practice often the electrician removes the fuse, and tells the DNO a new seal is required, not strictly legal, but unless there is a history of electric theft in the area the DNO often turn a blind eye.

However if one fuse feeds two meters then it seems likely the DNO will need to do some thing to allow your electrician to do his work, as simply pulling the fuse would remove power to some other persons property.

[GC1955]

Thank you Mr White. The reason I said that was because the heating engineer said "oh you have a 100A fuse..that means you probably have a 3 phase supply". I am not a tradesman and have no expertise in this area. I just thought it was an odd thing for him to say. Thank you for taking the time to reply to my post.

[ericmark]

Oh dear is your heating OK, some how doubt if he is an engineer, i.e. some one trained to level 5 or above, one would hope anyone who can get an engineering degree would realise a single fuse means a single phase.