RCD problem

[markymark31]

Evening all,

I've got a mobile piece of conveyor equipment which plugs in to a 16A 3ph socket in a warehouse.

So..... It's a socket, it must be RCD protected ?

But my mobile conveyor has a couple of inverters in its control panel which trip the RCD every time they are switched on.

Any advice would be appreciated ?

Thank you,

Mark

 

[Guest123]

Hey Mark.

How is the circuit installed??

If it's surface run in it's entireity or run in SWA or galv conduit and you label it for use then it does not need RCD protection. Also if the warehouse has a permanatly employed maintenence man who can be classed an instructed person this would negate the need for RCD protection.

Reg number - 411.3.3, P47.

Cheers

 

[markymark31]

Hi Lenny,

Thanks for the reply. I'd kind of ended up at the same reg as you.

The circuit is run in 3" galv trunking from the DB. There is no permanent maintenance man, but there are a few operators trained in the use of the mobile conveyor, they would count as instructed persons wouldn't they ? I can certainly put a label on the socket saying "mobile conveyor only" or something like that aswell.

This bit of the regs strikes me as a bit of a frig really. We've got a mobile conveyor plugged in to a socket. So there is a trailing lead (SY cable) with 400v running up it. In my head it should have an RCD to provide that extra protection should any damage occur to either the cable or our machine but the regs say that if you do the above you don't need it, it just seems odd, how do you see it ?

There is also another possible solution which would be to fit a less sensitive RCD say a 100mA or even a 300mA device. This would eliminate the nuisance tripping from the inverters but I am not sure what protection they would actually provide. I can't really find any reference in the regs other than 415.1.1 which refers to a rating of not more than 30mA being recognised as providing the protection required but it doesn't say you cannot fit a less sensitive device. 415.1.2 says that an RCD should not be the sole means of protection.

I would be interested to know your / anyone's thoughts ?

Regards,

Mark.

 

[Guest123]

Hey Mark.

In my opinion, our regs stop at the socket outlet, I dont feel we can be responsible for what the end user plugs into our socket.

So in this instance I would have to say that the socket outlet does not require 30mA RCD protection.

However I am of the same opinion as yourself when it comes to the trailing lead as if something did happen the fickle finger of blame would point straight at us. Although, the warehouse owner has a degree of responsibility to look after the welfare of his employees under the HASAWA 1974, if the eqiuipment supplied by him for the empolyees to use is unsuitable then it is up to him to rectify it.

Assaid though, technically according to BS 7671, the circuit does not need any form of RCD protection.

For peace of mind though as you said perhaps a 100mA TD RCD could be fitted.

Cheers

 

[lewlec]

Hi

does the conveyor have to be on a plug? Just wondering if you could replace the socket outlet for a rotary isolator? Then it becomes fixed equipment and depending on your earthing arrangements it may not need a rcd. Just a thought.

sorry.... just seen its a MOBILE conveyor

 

[ian.settle1]

Hey Mark.

In my opinion, our regs stop at the socket outlet, I dont feel we can be responsible for what the end user plugs into our socket.

So in this instance I would have to say that the socket outlet does not require 30mA RCD protection.

However I am of the same opinion as yourself when it comes to the trailing lead as if something did happen the fickle finger of blame would point straight at us. Although, the warehouse owner has a degree of responsibility to look after the welfare of his employees under the HASAWA 1974, if the eqiuipment supplied by him for the empolyees to use is unsuitable then it is up to him to rectify it.

Assaid though, technically according to BS 7671, the circuit does not need any form of RCD protection.

For peace of mind though as you said perhaps a 100mA TD RCD could be fitted.

Cheers

Don't think the client would be to amused with that type of reply "Nothing to do with us as we are only responsible up to the socket"

Find your self out of business very quickly with that attitude in the current climate.

 

[markymark31]

Hi Guys, thanks for the replies, all very helpful .......

For peace of mind though as you said perhaps a 100mA TD RCD could be fitted.

I think this is the way to go (maybe not a TD) but now I am a liitle confused over the testing side of things. I found this thread which sort of helps but I am I right in thinking that Table 41.5 in the regs is where I need to be looking ?

So for a 100mA RCD I can have a max Zs on that circuit of 500 ohms (as it is a 3ph supply) ? Is that right ? Typically the earth loop readings we get are only a few ohms, 500 sounds massive ? Have I got this right ? What about trip times etc.. Can anyone explain it in simple words I can understand ??

Many thanks,

Mark.

Edit : This might be for a TT system ?? Mine will be TN-C-S (PME) I guess ?? I am confused please help !!

 

[Guest123]

Don't think the client would be to amused with that type of reply "Nothing to do with us as we are only responsible up to the socket"

Find your self out of business very quickly with that attitude in the current climate.

So then Ian, do you take responsibility for every single piece of equipment and appliance that the user plugs into every socket you have ever installed?? I think not.

The OP's query was wether or not the circuit needed 30mA RCD protection, which in this case it doesn't.

How are we to know what will be plugged into that socket once we have gone and moreover how are we responsible for the condition of it??

As I said it is the responsibility of the employer to ensure that the equipment he supplies is fit for use, if there is a problem then we can be asked to deal with it.

If the machine cable was obviously in a dangerous condition and needed attention then I would not hesitate to remedy it. But who's to say next week that a different machine may be plugged into that socket would it then be our fault if something was wrong with that machine.....no.


What would your advice to the OP regarding his original query be then??

 

[Guest123]

Hi Guys, thanks for the replies, all very helpful .......



I think this is the way to go (maybe not a TD) but now I am a liitle confused over the testing side of things. I found this thread which sort of helps but I am I right in thinking that Table 41.5 in the regs is where I need to be looking ?

So for a 100mA RCD I can have a max Zs on that circuit of 500 ohms (as it is a 3ph supply) ? Is that right ? Typically the earth loop readings we get are only a few ohms, 500 sounds massive ? Have I got this right ? What about trip times etc.. Can anyone explain it in simple words I can understand ??

Many thanks,

Mark.

Edit : This might be for a TT system ?? Mine will be TN-C-S (PME) I guess ?? I am confused please help !!

Hey Mark.

Max Ze on TT system is 1667ohms, but a reading this high should never be accepted and the maximum accepted value is 200ohms.

Max Ze on a TN-S is 0.80ohms

Max Ze on a TN-C-S is 0.35ohms.

The max Zs values in table 41.3 apply to both TN-S and TN-C-S systems. Where as the max Zs values in table 41.5 apply to TT systems.

If any of your Zs values exceed the values for a TN-C-S in table 41.3 then additional RCD/RCBO protection is needed.

Cheers.