Correct size Cable and MCB for workshop

[GwBikes]

Hello Guys,
im new to form, so apolergise now for jumping straight into posting a topic. I have found lots of info on domestic wiring, but hoping someone can help with my commercial workshop.

I have 10 double sockets running on 4.0mm T+E in a radial circuit.
They go into a 32A MCB.

Sockets often used for running Angle Grinders, Welders, and Compressor which are high wattage.

Every now and then when running a few tools the main 100A MCB will trip, but the 32A MCB never goes out. Is the right MCB being used, or does the circuit need upgrading to cope with the power im using?

Thanks in advance.

 

[GwBikes]

Just to add..

The workshop is 1300 sqft which i belive is about 120m2. Been informed this makes a difference on load with cable runs etc?

 

[Taylortwocities]

That 100A thingy.

Are you sure that it is an MCB?

Perhaps its an RCD. Here's how to tell:

Untitled

• Taylortwocities
• 27 Mar 2010
• 43

Or post a piccy on here.

If its an RCD then you are looking at earth leakage problems, not over-current.


PS, if you want to add something to a post, try the EDIT key, it's fun!

 

[GwBikes]

Hello,
thanks for the reply.

Yes you are correct its a 100A RCD.

Sorry completely forgot there is a edit button, been years since i was active on a forum.

Thanks.

 

[Taylortwocities]

OK

So the 32A MCB is big enough for the job as it is not tripping.

Your problem is that one (or more than one) of the tools (or extension leads, or 110V transformers?) you are using has an earth leakage fault and this is tripping the RCD. This will trip if there is an earth leakage of (usually) 30milliamperes. (Your RCD will say something like 30mA or 0.03amp)

You would be advised to have the tools "PAT" tested or try and keep a note of which tool is being used when the RCD trips. You'll soon spot a pattern.

 

[GwBikes]

Thanks for the replies.

I traced back the earth wire from the CU and found it is just hanging down against the back wall of the workshop. Would this be causing the fault?

Should it be connected to a earth rod?
Earth wire looks as if its got 8 cores in it.

Thanks.

 

[EFLImpudence]

I traced back the earth wire from the CU and found it is just hanging down

Do you mean there is a CU in the workshop or do you mean the CU in the house?

against the back wall of the workshop. Would this be causing the fault?

Probably not. Are there any pipes nearby to which it may have been connected?

Should it be connected to a earth rod?

Don't know yet. Probably not as the RCD works. Does the end look like it has been connected to something?

Earth wire looks as if its got 8 cores in it.

It'll be 7.

How far is it from the house to the workshop?

 

[ban-all-sheds]

I traced back the earth wire from the CU and found it is just hanging down against the back wall of the workshop. Would this be causing the fault?

No, but it could cause people to die.

Should it be connected to a earth rod?

Don't know - what sort of supply do you have? Is it TT?

//www.diynot.com/wiki/electrics:earthing-arrangements

Anyway - doesn't really matter - what you must do is to get an electrician to come and sort out your earth connection, and until that is done do not use or touch anything electrical in the workshop.

Apart from anything else:

... commercial workshop ...

Electricity At Work Regulations etc - you should not be fiddling with any of this yourself.

 

[EFLImpudence]

... commercial workshop ...

Oh - Sorry, missed that bit.

 

[GwBikes]

Thanks for the detailed replies. I understand that should get a electrician to go over everything but without the funds to do so thought i would get some information from guys on here.

Just to confirm the workshop has its own supply comming in and through a meter. A phase is then taken from the 3 phase board and into a CU.

Appears to be running a TT earth system from the descriptions and photos in the link in previous post.

The earth wire which is dangling down the outside of building looks to have been connected to something in past, but was always hidden until recently when some bushes was cleared around the building.

From the photo of the TT system it seems the earth wire does need to be connected to a rod. If this is correct are they all standard or is there a certain size i need to get?

Thanks.

 

[EFLImpudence]

are they all standard or is there a certain size i need to get?

It doesn't matter what size electrician you get.

 

[Spark123]

You can't just go knocking any old earth rod in the ground and connecting to it, it needs to be tested properly usong a calibrated earth fault loop impedance tester, you need an electrician.