Info on a dedicated circuit for a welding machine required.

[JohnD]

Derivation:

Electrical
Execution

Electr...
...cution

Electrocution

I suppose you could argue that "hanged by the neck until you are dead" should include "wearing an uncomfortably tight shirt collar"

 

[EFLImpudence]

The Oxford English Dictionary seems to be staffed by people who don't really understand - literally.

 

[333rocky333]

Maybe I should put a 45A RCD in the garage CCU and protect it with a 50A MCB in the other CCU that feeds it. .

NO. As I said two RCDs in line is pointless. RCDs do not trip on over current, they protect against imbalance typically caused by leakage to earth. The current rating is the safe load not a trip.

Rubbish, the current rating on the device 45A is the trip rating, it is obvious he means an RCBO which is a form of RCD

 

[333rocky333]

The current rating is the safe load not a trip.

And if you mean Main switch type Rcds, surely the rating in the OPs boards which he says, one has 63A and the other 80A Are the MAXIMUM load, NOT the safe load.
No wonder we need flame retardent boards now!

 

[JohnW2]

And if you mean Main switch type Rcds, surely the rating in the OPs boards which he says, one has 63A and the other 80A Are the MAXIMUM load, NOT the safe load.

I think you're quibbling a bit - since, if running an RCD at its rated 'maximum current' was 'not safe', I think something about the stated ratings would be seriously wrong!

Kind Regards, John

 

[RF Lighting]

Yes I don't think RCDs have an intermittent duty cycle rating!

 

[winston1]

Rubbish, the current rating on the device 45A is the trip rating, it is obvious he means an RCBO which is a form of RCD

Obvious to whom? No one else on here has assumed he means RCBO. Anyway you must never assume with electrics if you want to live to enjoy retirement!

 

[Isol8or]

And if you mean Main switch type Rcds, surely the rating in the OPs boards which he says, one has 63A and the other 80A Are the MAXIMUM load, NOT the safe load.
No wonder we need flame retardent boards now!

Maybe I never explained it very well but it is not that hard to see what I need.
The set-up so far is a 63A RCBO from an unprotected way in the CCU that feeds the garage CCU. I am wondering if I would be allowed to use a MCB instead because the cable is about 5" behind the wall and its clipped inbetween floor joists in the middle which is 4" away from ceiling and floor. I have 8" joists and 6" walls plus 1 1/2" insulated plasterboard in front. If I went for this option I would have a CCU with RCD protection for the circuits in the garage. Another reason I think this would be a good idea is that I plan to build a shed in the garden and then I could protect the circuits going to the shed seperately from the garage circuits. What is your view on this set-up?

 

[RF Lighting]

You'd be best using a BS88 or BS1361 cartridge fuse to supply the sub mains given the proposed loads, and then arrange RCD protection in the garage CU as and where required.

 

[333rocky333]

Obvious to whom? No one else on here has assumed he means RCBO. Anyway you must never assume with electrics if you want to live to enjoy retirement!

No one assumed, as I say it was obvious
1, For one he has a CU board with a 63A Rcd main switch, how on earth could he fit anything other than an RCBO without butchering the board.
2, Apart from an Rcbo what other RCD exists in a 45 amp rating

 

[Isol8or]

No one assumed, as I say it was obvious
1, For one he has a CU board with a 63A Rcd main switch, how on earth could he fit anything other than an RCBO without butchering the board.
2, Apart from an Rcbo what other RCD exists in a 45 amp rating

I don't have the CCU, the whole question is hypothetical, the only thing that can't be changed is the 16mm SWA.

 

[Isol8or]

You'd be best using a BS88 or BS1361 cartridge fuse to supply the sub mains given the proposed loads, and then arrange RCD protection in the garage CU as and where required.

The CCU is already protected by a 80A DP switch fuse by the way, should I put another one in to protect the garage CCU?
It seems a bit overkill to me, I mean the welder has 25A protection built in with a 32A MCB and there's a 63A RCBO behind it ready to trip if any or all the circuits in the garage fail to trip via their respective MCB's. The washing machine & tumble dryer might at some random period for a short time use 25-26A combined.
If there is a requirement to add another fused switch for the garage, how would it be wired? From the SWA feeding the CCU or from the unprotected way in the CCU, is that even possible?

 

[EFLImpudence]

Fuses and MCBs protect cables - not CUs.

RCDs protect people.

 

[RF Lighting]

You can do what ever you want. It's not going to affect me. Using a cartridge fuse rather than a circuit breaker to protect the submain will guarantee discrimination and give you a much more reliable installation, but if you want to use a circuit breaker that's entirely up to you.

How it's wired is up to your electrician to decide, but normally a switch fuse henleyed of the incommer is the best way to achieve this.

 

[Isol8or]

You can do what ever you want. It's not going to affect me. Using a cartridge fuse rather than a circuit breaker to protect the submain will guarantee discrimination and give you a much more reliable installation, but if you want to use a circuit breaker that's entirely up to you.

How it's wired is up to your electrician to decide, but normally a switch fuse henleyed of the incommer is the best way to achieve this.

Ok I'm not saying your not right, don't be so touchy, I'm just giving more information about what the situation is incase it makes a difference to the design in regards to safety. While I'm at it I might as well explain that the new CCU will be in an extension which is Henley blocked and has the 80A switch fuse I mentioned. It will be interesting to see if the electrician chooses to use another switch fuse or rely on the MCB in the RCBO.