>30m distance from meter to consumer unit.

[Omm4r1]

Hi guys,

a baffling question (well in my mind anyway). I got called to have a look at some wiring for an old Victorian built property, its a friends property and as I only stick to domestic installations he wanted me to have a look at this commercial use building. Basically it's got 5 floors starting with the lower ground floor which is where the meters are. As all the floors are seperately rented out, he has the top floor spare and wants to convert this in to a residential apartment.

Bare in mind this building is very tall and is pretty huge with high ceilings.

Now ow I know in a domestic installation if the consumer unit is over 3 meters away an 80amp isolator would be needed and then you could carry on as long as it was within a reasonable amount of distance, taking into account voltage drop and other factors.
This property has the meter in the lower ground level which is the cellar and the consumer unit would obviously go in the top level. This I worked out would be over 30m in length.

my question is, what is the way around this? It is a three phase supply and he said he would be getting a complete separate meter just for this apartment. But doesn't wants to install this in the cellar.

How would one get around the issue of voltage drop and stuff??? As this would be too far for the cable presuming 25mm tails.

thanks in advance guys

Ommar

 

[Sintra]

If he wants the meter moving to the top floor then only the DNO can do this. If the meter is staying in the cellar fit a fused isolator beside it and run a SWA to the consumer unit. Why would you consider 25mm tails.

 

[derek]

If the CU is over 3m from the head then a circuit protective device may be required, an isolator is not necessarily one, what BS number is your isolator?

 

[Omm4r1]

Thanks for the reply Sintra, it will be the DNO that will be doing the meter but the meter will be in the cellar and due to the length the cable has to run (30m) I thought the 25mm would be sufficient enough.
Am I wrong in thinking this? Can I use a smaller cable?

 

[Omm4r1]

Derek, I'm not sure as this is only a thought so far I need to collate my information and get back to him with his options the length between CU and meter is just over 30m

 

[Sintra]

Thanks for the reply Sintra, it will be the DNO that will be doing the meter but the meter will be in the cellar and due to the length the cable has to run (30m) I thought the 25mm would be sufficient enough.
Am I wrong in thinking this? Can I use a smaller cable?

Cable size would need to be calculated taking into account fuse rating in isolator, length, installation methods and voltage drop. Time to get your calculator out

 

[Omm4r1]

Cheers guys appreciate all the help

 

[davesparks]

You will be installing a sub-main from the cellar to the flat, this is a distribution circuit which you may not have come across before if your work is purely domestic.

I apologise now if I am teaching you to suck eggs here but from what you have posted so far I think this may help.

A sub main is in principle no different to a radial circuit which feeds a single point, such as an immersion heater supply or cooker supply, but usually a bit bigger.

You will need to establish how big a supply you need to the flat using diversity calculations and a bit of common sense.
You can then select a suitable sized sub-main.
I'll be surprised if you need more than 40A but personally would run a 63A supply minimum to allow for any future increase in load (eg replace gas cooker with electric)

Then you can carry out the cable size calculations as per usual.

It is advisable to use a switchfuse with bs88 fuse rather than an MCB for the OCPD.

You could use T&E cable but SWA is far more advisable, it will negate any need for an RCD on the submain. Also the cpc in large T&E will likely be too small, especially if main bonding is required. 3 core SWA will obviously give you a bonding conductor in the cable without having to run a seperate one. If no bonding requirement then 2core SWA will likely be fine.

 

[Omm4r1]

Dave sparks you are a true gent, thanks

 

[Octopus]

Dave sparks you are a true gent, thanks

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