MCB and RCD ratings

[Haz]

In my workplace there has been periodic complaints of a particular room losing all power whilst they are working. I have heard the electricians have been in and checked things out and have given the electrical system a clean bill of health. They reckon it could be a particular piece of equipment causing the loss of power, however the manufacturers of the equipment say there is nothing wrong with the equipment.

Having spoken to my boss he has another theory- he reckons the MCBs and RCBOs used in the room may be incorrectly rated for this type of equipment which uses an isolation transformer which has a high inductance. He says you get MCBs and RCBOs which are rated as A,B,C and D but only C and D type are rated for high inductance equipment such as ours with the isolation transformer. Does anyone have any information regarding the A B C D rating of the MCBs and RCBOs which could shed some light on this problem.

 

[Andy™]

instant trip:

B will trip at 3-5x rated current

C 5-10

D 10-20

note: you cannot simply change a B type for a C or D

what does the manufacturers instructions for the equipment say about what breakers should be used? and what is currently used?

 

[green-hornet]

Type B which is what may be fitted in the room in question would not handle large inrushes, the most common to be fitted are Type C.

The differences in all types is down to the curve characteristics.

Some breakers will "hold for longer times" than others in what could be concidered a fault and is designed to do so for equipment that uses above average currents during startup.

 

[Nicky Tesla]

It could well require a type c instead of a b. Many large welding plants can require this.

To change it to a c type you will need to check to see if the Zs readings are still low enough.

Why not try starting the machine repeatedly to see if it is this that trips the breaker.

 

[Blue Fox]

If there is quite a few desktop pcs in there that could be the cause, there was a similar problem in a factory I worked in quite a few years ago and one of the offices kept tripping its RCD. I didn't work on the fault but it was traced to the earth leakage of the pc's power supplies which all added up tripped the rcd.

 

[batty]

It could well require a type c instead of a b. Many large welding plants can require this.To change it to a c type you will need to check to see if the Zs readings are still low enough.

Why not try starting the machine repeatedly to see if it is this that trips the breaker.

Where have you been Nicky on holiday. I would disagree with type C for welding equipment should be D type.

Batty

 

[Andy™]

Where have you been Nicky on holiday. I would disagree with type C for welding equipment should be D type.Batty

i have a few welders and compressor running happily on a C type...

 

[Haz]

Thanks for the information, we've not yet checked what is in there just yet. I was unaware of the A B C D ratings of these units and just wanted a bit of background before we go in and put our theory forward, will keep you posted.

Cheers

 

[Brian 157]

Are they MEM "Memshield" RCBOs of about 10 years old by any chance? There was a design fault with these and certain types of cordless phones and walkie-talkies cause them to trip if used nearby... I had great "fun" chasing a non-existant fault on an installation using these RCBOs a few years ago, eventually solved after a chance conversation with an MEM rep.

 

[a1]

Thanks for the information, we've not yet checked what is in there just yet. I was unaware of the A B C D ratings of these units and just wanted a bit of background before we go in and put our theory forward, will keep you posted.Cheers

Good Man.

 

[Andy™]

Thanks for the information, we've not yet checked what is in there just yet. I was unaware of the A B C D ratings of these units and just wanted a bit of background before we go in and put our theory forward, will keep you posted.Cheers

since we want to know everything... whats the current breaker/rating type and rating of equipment?

 

[Nicky Tesla]

Where have you been Nicky on holiday. I would disagree with type C for welding equipment should be D type.Batty

Holiday, if only batty, ive been busy rewiring igloos, been absolutely snowed under