Electrical Discrimination Issues

[Contractman]

I have an electrical installation in a garage. The supply from the house to the garage is protected by a 80 Amp 100mA RCD.

When I use certain tools in the garage, mainly an orbital sander and a finger grinder the main RCD in the house trips and plunges the place into darkness, seemingly by passing the local MCBs in the distribution board in the garage. The ring is protected by a Wylex B32 NSB breaker.

The tools in question seem to operate for a short period of time but after say 5/10 minutes they trip the RCD each and every time until I have to stop using them.

I assume they are not faulty as they work in the house for unlimited amount of time.

Do I need to change the type of MCBs in the local board for something more or less sensitive, with a view to the local protection operating, or is this giving to give me further nuisance tripping?

I changed the RCD in the house recently from a 30mA unit to the 100mA and I still have the same problem..

 

[Pete999]

I have an electrical installation in a garage. The supply from the house to the garage is protected by a 80 Amp 100mA RCD.

When I use certain tools in the garage, mainly an orbital sander and a finger grinder the main RCD in the house trips and plunges the place into darkness, seemingly by passing the local MCBs in the distribution board in the garage. The ring is protected by a Wylex B32 NSB breaker.

The tools in question seem to operate for a short period of time but after say 5/10 minutes they trip the RCD each and every time until I have to stop using them.

I assume they are not faulty as they work in the house for unlimited amount of time.

Do I need to change the type of MCBs in the local board for something more or less sensitive, with a view to the local protection operating, or is this giving to give me further nuisance tripping?

I changed the RCD in the house recently from a 30mA unit to the 100mA and I still have the same problem..

There is an earth fault on either one of your tools or the associated wiring, an RCD trips when there is a inbalance, ie a fault to earth, and an RCD does not provide overload protection, it isn't bypassing the CBs it only doing its' job in protecting you from a dangerous fault, don't swap anything, get an electrician to test the wiring and the tools used there. To help you could check the Tools for damage to the flexes, plugtops etc, but lt sounds like one of your tools is working OK when it's coo; but as you use it, it heats up and expansion causes the innards to expand and produce the fault that trips the RCD.

 

[Sintra]

I take it the 80A 100mA RCD serves both the house and the garage. A RCD works by sensing an imbalance between live and neutral hence why the MCB's don't trip. I wouldn't assume that the tools are good just because they work somewhere else unless they have been properly tested. Why on earth did you change a 30mA unit to a 100mA unit? Doing that has put you and anyone else at greater risk as 100mA RCD's are not made to provide additional protection required for socket outlets etc.

 

[Lucien Nunes]

As per Pete above there is probably a latent fault, quite possibly a neutral-earth fault on one of the garage circuits. The fault may be there all the time but it only passes enough current to trip the house RCD when the load of one or more power tools is present within the garage, hence the tools work OK in the house. Electrical testing on the garage circuits and submain would be my next step.

Also as above, re-fit the 30mA RCD in the house. The 100mA does not provide protection against shock, so you have downgraded your installation to non-compliance.

 

[telectrix]

as above, but also note that it would be better to feed the garage from a non-RCD circuit and then firt a 30mA RCD in the garage. then it would trip in the garage, not the house. this assumes that the feed from the house does not require RCD protection in itself.

 

[Wilko]

Hi - agree with Folks above, there’s a fault to be found. Please you need to restore the 30mA RCD for the house as you’ve now made the installation non compliant and removed a safety net. With a fault known to be present ... oh dear!

 

[snowhead]

Are both the sander and grinder in the garage being used in an extension lead or directly in a 13amp socket?
Are they always plugged in the same socket?

 

[Vortigern]

Any pictures possible maybe of your main board and local board in garage?

 

[Contractman]

Hi - agree with Folks above, there’s a fault to be found. Please you need to restore the 30mA RCD for the house as you’ve now made the installation non compliant and removed a safety net. With a fault known to be present ... oh dear!

I asked for a bit of electrical advice mate, not some childish patronising comments!

 

[Pete999]

I asked for a bit of electrical advice mate, not some childish patronising comments!

Can't see any Childish Patronising comments Contractman. You got lots of good advice from what I can see.

 

[westward10]

I asked for a bit of electrical advice mate, not some childish patronising comments!

I too am not seeing any issues. @Wilko is one of our most respected members, if you have any issues with a post you should report them.

 

[Wilko]

I asked for a bit of electrical advice mate, not some childish patronising comments!

Sorry for giving that impression.

 

[DPG]

I wouldn't worry about it Wilko. Unless being concerned for someone's safety is something to apologise for.

 

[Pete999]

Sorry for giving that impression.

Nothing to apologise for Wilko as far as I can see.