House/workshop breaker problem.

[PCUK]

Our bandsaw gets damp in the winter and occasionally blows the RCCB. Could I fit a more sensitive breaker at the saw to blow before the main breaker in the house. The consumer box for the workshop is separate from the house power so no affect on the house power. Just like to avoid the walk to and from the house when it blows. Thanks

 

[matthewriches]

Generally in a commercial setting would be fitted with a D curve breaker with suitable discrimination to stop the same issue as you have. Little more difficult in a house without time delay, etc.... When you say main breaker in the house, do you mean another RCCB, an RCD, an MCB? Getting damp, I'd guess the main house board RCD is tripping unless you're all on RCBOs or similar?

 

[VicS]

Generally in a commercial setting would be fitted with a D curve breaker with suitable discrimination to stop the same issue as you have. Little more difficult in a house without time delay, etc.... When you say main breaker in the house, do you mean another RCCB, an RCD, an MCB? Getting damp, I'd guess the main house board RCD is tripping unless you're all on RCBOs or similar?

Doesn't "D curve breaker " refer to an overcurrent trip? ( MCB or RCBO) I think PCUK is probably referring to RCDs

If the RCD which supplies the workshop is a separate one from the house RCD(s) I think it could be changed to a 100mA one and the normal 30mA one retained in the workshop provided it protects the whole workshop.

Fitting a lower rated RCD locally would probably lead to an unacceptable number of nuisance trips

I wonder when the bavd saw was last PAT tested ?

I also wonder it the electrical supply, in particular the earthing arrangements, comply with the regs for supplies to outbuildings.

 

[Graham376]

An underground cable doesn't need an rcd at the consumer unit and, as mentioned above, a type C or D breaker should be OK.

 

[matthewriches]

Yes Vic, the "type" generally refers to an over current protection device so MCB, RCBO, etc but not sure yet how OP has his system fully rigged as mentions RCCB then "Breakers".

When doing outbuilding or external power work, I generally run with SWA cable everywhere then use local 5mA or 30mA earth leakage protection as required, where the main run from the DB generally sits on a type S time delay earth leakage device with suitable over current protection but as mentioned above, you can run without earth leakage protection on the feeder DB if suitable mechanical protection but for the little extra cost, it's worth just sticking a time delay in.

In the OP case, if workshop is fed from it's own supply on SWA with it's own earth leakage protection device, he could forego the feeder DB earth leakage protection or swap it out preferably for a time delay, then ensure suitable life saving local earth leakage protection is used in the workshop, 30mA or 5mA with correct type and rating of over current protection.

Changing out a 30mA to 100mA in the house, if indeed that is the current setup may or may not help. Not uncommon for setups like this to cause issues when carrying out electrical inspections as the 100mA can, but not always, still trip first.

A common cause of motors to blow out in cold and damp is due to ingress into or between windings or insulation protection. So could cause either the earth leakage to drop out or the over current protection to fall over depending on what fault is present.

 

[Old Harry]

An underground cable doesn't need an rcd at the consumer unit and, as mentioned above, a type C or D breaker should be OK.

I had the same issue with a 110v transformer, swapped out the std "B" type mcb for a C type, problem solved

 

[PCUK]

Should have said, nothing in the main box can be changed. I'll have to check the spec' and actual type of main breaker. Thanks.

 

[doug748]

Our bandsaw gets damp in the winter and occasionally blows the RCCB. Could I fit a more sensitive breaker at the saw to blow before the main breaker in the house. The consumer box for the workshop is separate from the house power so no affect on the house power. Just like to avoid the walk to and from the house when it blows. Thanks

I have a similar problem which sometimes trips the house breaker; it is hyper sensitive anyway and quite capable of tripping on it's own.

I found that a very firm press of the machine off switch generally prevents the difficulty, My guess is that the glancing nudge, that we tend to use, allows the contacts to bounce which causes the trip - this is only a theory.

 

[lw395]

Our bandsaw gets damp in the winter and occasionally blows the RCCB. Could I fit a more sensitive breaker at the saw to blow before the main breaker in the house. The consumer box for the workshop is separate from the house power so no affect on the house power. Just like to avoid the walk to and from the house when it blows. Thanks

You should get the saw leakage tested and sort out heating or a dehumidifier in your shed by the sound of it.

 

[lw395]

I have a similar problem which sometimes trips the house breaker; it is hyper sensitive anyway and quite capable of tripping on it's own.
...

That very probably means you have a continuous leakage of several mA using up some of the 30mA threshold

 

[Alex_Blackwood]

You should get the saw leakage tested and sort out heating or a dehumidifier in your shed by the sound of it.

+1 The problem is the machine not the circuit or the protection, that is doing what it was designed and installed to do. . Could possibly be a "Leaky Capacitor " on the motor, Maybe. Needs checking, fix the problem not the symptoms!