RCDs on Machines

[Russell Moss]

I am looking at installing electrical supplies for a series of equipment that form a DPF test bed. There will be five individual machines needing 3 phase supplies via a plug and socket arrangement, this has been specified by the manufacturer, isolators are not allowed. The biggest supply is only 7 amps so am assuming I have to adhere to regulation 411.3.3 requiring RCDs on sockets below 32amps. There is the option of doing a risk assessment but dont think this would help in my case.

My concern is nuisance tripping, or even that natural earth leakage could mean the RCD will not work.

Any advice gratefully accepted

 

[telectrix]

you need a RA to establish whether or not RCD/s would interfere excessively with production.

 

[Russell Moss]

you need a RA to establish whether or not RCD/s would interfere excessively with production.

Thanks Telectrix, so the RA concerns the possible disruption to the process rather than the equipment? I was concerned about Exposed Conductive Parts.

 

[telectrix]

Thanks Telectrix, so the RA concerns the possible disruption to the process rather than the equipment? I was concerned about Exposed Conductive Parts.

exposed conductive parts should be earthed and so ADS will apply. the RCD is for contact of body with live parts, nothing to do with exposed conductive parts ( unless being used for fault protection in the case of excessively high Zs )

 

[Russell Moss]

exposed conductive parts should be earthed and so ADS will apply. the RCD is for contact of body with live parts, nothing to do with exposed conductive parts ( unless being used for fault protection in the case of excessively high Zs )

Thank You

 

[loz2754]

The risk assessment is supposed to be to decide on whether an RCD is required or not.
Not whether fitting one will disrupt a process or not. If it's required, but you think it might interrupt a process, then you would have think of a different approach to powering the equipment that does not require an RCD.

 

[DPG]

Why do they insist on having no isolators?

 

[Russell Moss]

The risk assessment is supposed to be to decide on whether an RCD is required or not.
Not whether fitting one will disrupt a process or not. If it's required, but you think it might interrupt a process, then you would have think of a different approach to powering the equipment that does not require an RCD.

Thank You Loz2754. Unfortunately I cant think of any other approach that would not contravene the regulations. I think a call to the NIC might be needed.

 

[Russell Moss]

Why do they insist on having no isolators?

I have no idea really. We work for a company who are sourcing the equipment. The only thing I can think of is the units are being imported from America (yes have checked they are compatible for the UK market) and they are plug and play into each other so I guess its makes the whole install cleaner if they plug into the mains also. I wouldn't want to cut the plugs off and connect direct in case it caused warranty issues.

 

[Mikegh]

Probably don't want operators/randommers switching off machines at isolators

Emergency stops if required and isolation/switching off for maintenance at the plug and db

 

[Mikegh]

If the equipment is fixed in position there's no benefit to having isolators over plug/sockets

That's probably the thinking

They're probably getting a bit screwed up on the Rcbo requirement, I'm not familiar with bs6761 so don't know about that

 

[DPG]

If the equipment is fixed in position there's no benefit to having isolators over plug/sockets

That's probably the thinking

They're probably getting a bit screwed up on the Rcbo requirement, I'm not familiar with bs6761 so don't know about that

BS7671 has specific requirements for RCD protection on socket outlets.

 

[Mikegh]

BS7671 has specific requirements for RCD protection on socket outlets.

Yes and that's where they're making the mistake I think

They don't want the isolators but they won't want the Rcbos either

 

[DPG]

Yes and that's where they're making the mistake I think

They don't want the isolators but they won't want the Rcbos either

But it's the manufacturer stipulating no isolators, and the OP who is reluctant to fit RCD protection.

OP, is it really likely this machinery will trip a 30mA RCD?

 

[freddo]

I wouldn't expect 30+mA earth leakage on normal equipment drawing such low currents. If the equipment really does have high protective conductor currents, extra care needs to be taken. There is some information here I can't look at the regs book myself as it is currently being borrowed.

I can't really think of a good reason not to fit RCD protection.
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