MCB tripping

[Robo]

B32 breaker feeding a 6mm swa radial which loops into one garage and then to the next. The garage has a 30ma RCD main switch. When a welder is plugged in it trips the 32a breaker at the origin?? Y would it not trip the mcb in the RCD garage board.?? i thought about changing the B to a C32.?? Thanks

 

[ian.settle1]

Due to the surge current when you start a welder or transformer normally a C or D type is fitted.

 

[telectrix]

what mcb is in the garage? remember if you fit a c type, your max. Zs is halved.

 

[truckster]

what mcb is in the garage? remember if you fit a c type, your max. Zs is halved.

Unlikely to be a problem with a 30mA RCD

 

[Robo]

B32 at main board.
6mm swa to adap box in 1 garage which spurs to a main sw consumer unit.
then from adap box it ends up in garage where problem is. Its a B32 breaker
in Rcd garag3e board.

 

[telectrix]

RCD is in garage. it's the house MCB he wants to replace. hopefully this is not RCD protected or he will have no discrimination and problems with house RCDE tripping with a garage fault.

 

[truckster]

Yes, reread it, but changing the MCB in the house will only push the problem to the garage. He'll need to change both MCB's to achieve discrimination and protect against surges. Not got my book handy so perhaps 40A type d in the house and a 32A type c in the garage? If Zs is a factor then he'd need a delayed RCD at the origin.

 

[pushrod]

You almost certainly have enough slack in the CCC of the 6mm to up to a 40A B type mcb, possibly even a 45A ( if you can get them) dependent on installation method, might be worth a try especially if the Zs is going to be a problem with the C type breaker

 

[telectrix]

i don't like the idea of relying on RCDs as a primary means of fault protection. it's like sod the design, bung in an RCD if the loop impedance is high. ideally, a 40A type c in the house with a 32A type c in garage to give discrimination. also, it has not been stated what earthing arrangements apply to the garage. ( i assumed it was TN exported from the house )

 

[Robo]

TNC-S supply-plastic water in each garage.The main board in the house is 16th. The garages are wired in a radial from a B32 which is RCD protected . I assume it been put on rcd because it runs in Tand E through the house. The cable run is as follows.

(all in 6mm 3c swa)House to brick garage where it goes to adap box. connector blocked and out again to next garage. ( Iv been asked to install db n lights n scokets in first garage.

Rcd board in second garage with B32 for ring main.

So chance the main supply breaker to a B40 or C 40? Iv explained about Descrimination of RCD but the customer says he doesnt mind??or is this a must.

If its a must are there time delay RCBOs out there?? or i would get time delayed rcd and put in enclosure.

Suggestions. Thanks

 

[pushrod]

If the T&E is surface mounted it doesn't need an rcd . There is no law afaik that says there can not be 2 rcds on the same circuit, but it does smack of amateurism/cost cutting etc and will be confusing if there is a trip and also mean that the rcds can't be tested without getting a screw driver out - it is not the way i would go.
Never come across a time delay rcbo.

If there is an rcbo at the main CU then there doesn't have to be an rcd at the garage - just makes resetting more difficult.

 

[Robo]

just been to check more in depth. Its swa right from main board. so im gonna swap it to unprotected side then you get descrimation so only the garage rcd trips. And to stop the mcb trippin try a c40 and ch4eck zs values.

 

[i=p/u]

you can do all these checks before you change anything, £5.00 and il do them for you