Could use some help with wiring

[Sean9461]

hi,

I'm looking for some help in regards to working out the load calculation of a wire.

I'm pretty sure it should be ok but I just want to double check.

I have an outhouse workshop and have a mcb in my main house.

I had an electrician in to install a sub panel in the outhouse.

He installed a 10mm2 cable which only extends 3m max to the sub panel.

He installed a 50a breaker in my mcb leading to the sub panel.

The mcb has a rcd in it.

Now I'm aware about having to get an electrician in however my question is very simple.

The 50a breaker I would like to upgrade to 80a.

To run more load as I run a business from home several servers etc.

From all calculations I have done the 10mm2 cable over 3m should be able to handle 80a.

So I should be able to simply switch out the breaker for a 80a.

I would just like to confirm this with you guys. Can anyone confirm that this should be ok?

I really don't plan on paying or even getting someone to drive here to simply install a new breaker for me when it's literally as simple as switching a 3 pin plug.


Cheers

 

[telectrix]

you can't fit a 80A breaker to a 10mm cable. 50A is the correct size. last time i saw a 80A on a 10mm was the morning after the Fire Brigade had attended. and it was bloody boxing day at a local cattery. poor buggers had no heating in the cages till after i'd been and sorted it asll out.

 

[Sean9461]

What is the calculation you use to work out the breaker size then?

As I used a website that works out the calculation for you and it came back saying over 3m at 10mm2 can carry 80a

 

[Sean9461]

I used this:

230v
Over 3m
80a

http://www.solar-wind.co.uk/cable-sizing-DC-cables.html

 

[Sean9461]

Although, now I realise that it's for DC.

How do I work out load for AC

 

[Pete999]

Kin ell

 

[Andy78]

I don't really know where to start, apart from, no you can't do what you are planning without it being dangerous.
Get an electrician in to do a load assessment for you and see what you actually require. If you really do need more than a 50A supply I'll be gobsmacked. If you do actually require a 80A supply out to your outhouse then it's probably time to contact the DNO to uprate your service cable.

 

[Adie moore]

what Pete said

 

[bigspark17]

You would be putting the property and its occupiers at risk if you do this!!! Why not get a local electrician in to upgrade the submain cable and breaker and give you the proper documentation for it?

 

[Darkwood]

As above, you need to get the job re-assessed, also another point is your incoming supply, have you contacted your supplier to enquire what allowance and DNO fuse rating you have, it may be that you have a 60, 80 or 100amp service fuse which may limit you.

I also ask you why you want to upgrade to an 80 amp, I suspect the rcd is tripping with all the servers designed earth leakage, was the Electrician made aware what type of loading was going on this circuit as I suspect this is designed wrong if that is the case, so can you confirm why you want to increase to a 80amp when from what you say, I find it hard to justify an 80amp supply for a few servers unless your running a big office block.

 

[Octopus]

Back to the op, what makes you think you need 80A, that's a lot of servers, or is it lamps?

 

[Sean9461]

I may have worked out total load wrong.

I have a farm house and have a new extension on the outhouse which i plan on adding extra rings eventually as well to have a seperate flat for mother in law.

I'll get an electrician out then

Cheers

 

[rolyberkin]

Back to the op, what makes you think you need 80A, that's a lot of servers, or is it lamps?

Ha, I thought that!

 

[westward10]

Seen 80A mccb but not mcb?

 

[Pete999]

Seen 80A mccb but not mcb?

Stop it you bad man

 

[Octopus]

So you have a house, with an office and you are planning to add an annex..... Best you get this all laid down as you may need a supply upgrade....

 

[Sean9461]

Yeah it's more complicated than I thought then. I'll get an electrician in with the builders at the same time.

Thanks for help

Appreciate it

 

[davesparks]

Seen 80A mccb but not mcb?

MCBs are available up to 125A, above 63A they are normally three units wide (27mm) instead of the standard 2 units (18mm)
The only standard DB I know of which can take them is the 200A (might be 250A) memshield 3 boards which can have a number of 27mm ways as required.

Also see the Schneider (Merlin Gerin) C120H range of mcbs.

Ive got a 125A C type Terasaki sitting on the bench in the workshop at the moment,

 

[Sean9461]

I'm getting someone out for a quote tomorrow and builders coming out today.

I have what may be a stupid question though guys,

If a breaker is rated for 50a and it's a type b. I've read type bs overload at 2-3x its rated value?

So can you run more than 50a through a breaker?

As off my 50a breaker I have a 16a breaker on my sub panel. Which if I worked it out properly would be max 3680w. Now I have several servers on this circuit well, 8 servers each with a 600w psu.

Now psus hardly ever draw their full rated power but my question is,

If they draw 4000w in total for a couple of hours will the breaker be ok or will it instantly trip as soon as I go 1 watt over 3680w?

Cheers

 

[Octopus]

If you try and run a breaker over its limit for a period it will

A. Trip

and

b. Fail after a while