3phase RCCB used no Neutral

[Savdar1810]

Question for someone... recently inspected a 3phase 415v supply socket and noticed it's protected by a 40amp 30ma rccb... Income supply only has 3phases and earth and on socket side requires neutral... Surely this RCCB isn't doing it's job if the neutral is not fed through protective device? It'll just be acting as MCB with neutral from load and plug going no where? Looking for advice on fixing issue? Will I need to run neutral from busbar or can i just replace with MCB and leave N?

Picture attached

Thanks

 

[Lucien Nunes]

Oooh that's nasty. No problem with the RCD functionality as such; it will work correctly provided that all conductors of the circuit go through it, whether that be 3P+N or just 3P.

The problem is having a 3P+N+E socket without the neutral connected. If someone plugs in equipment that requires a neutral, bad things could happen, including going bang and giving out lots of smoke. If the socket was only intended for equipment that does not need a neutral, it should be a 4-pin 3P+E socket so that this mistake cannot be made. If the 5-pin socket is to remain, then the neutral must be connected up.

 

[Savdar1810]

Question for someone... recently inspected a 3phase 415v supply socket and noticed it's protected by a 40amp 30ma rccb... Income supply only has 3phases and earth and on socket side requires neutral... Surely this RCCB isn't doing it's job if the neutral is not fed through protective device? It'll just be acting as MCB with neutral from load and plug going no where? Looking for advice on fixing issue? Will I need to run neutral from busbar View attachment 47804 or can i just replace with MCB and leave N?

Picture attached

Thanks

Going to replace rccb with MCB I think as no point in having rcd without neutral. It's only for industrial heaters

Oooh that's nasty. No problem with the RCD functionality as such; it will work correctly provided that all conductors of the circuit go through it, whether that be 3P+N or just 3P.

The problem is having a 3P+N+E socket without the neutral connected. If someone plugs in equipment that requires a neutral, bad things could happen, including going bang and giving out lots of smoke. If the socket was only intended for equipment that does not need a neutral, it should be a 4-pin 3P+E socket so that this mistake cannot be made. If the 5-pin socket is to remain, then the neutral must be connected up.

Cheers for the reply mate. Yeah test function works okay. Just wanted a second opinion. I checked load end socket and it's just 3p&E so it's okay that way...but like you said if something with a N get a plugged in...not good.

 

[Deleted member 26818]

Why would you replace with an MCB?
It’s a socket, and I assume it’s rated at 32A and requires RCD protection unless there’s a documented Risk Assessment indicating RCD protection is not required.

 

[Bobster]

Going to replace rccb with MCB I think as no point in having rcd without neutral. It's only for industrial heaters.

Why would you replace the Rccb, if it tests as functional?

 

[Savdar1810]

Why would you replace the Rccb, if it tests as functional?

I'm not rob. Just gonna replace 5pin socket and update RCD to a new version I think.

 

[Jim Cartledge]

Oooh that's nasty. No problem with the RCD functionality as such; it will work correctly provided that all conductors of the circuit go through it, whether that be 3P+N or just 3P.

The problem is having a 3P+N+E socket without the neutral connected. If someone plugs in equipment that requires a neutral, bad things could happen, including going bang and giving out lots of smoke. If the socket was only intended for equipment that does not need a neutral, it should be a 4-pin 3P+E socket so that this mistake cannot be made. If the 5-pin socket is to remain, then the neutral must be connected up.

I couldn't agree more! I would never consider connecting 3P+N+E socket without connecting the neutral, even if its usual intended use was to supply equipment which didn't use neutral. It may be needed some day. As Lucien points out BANGS & SMOKE could be the result.

 

[Spectric]

Hi

If my electrical theory serves me correctly then a three phase RCD will not require a neutral because at any point in time the three phase voltages will sum to zero and therefore the currents. If one phase leaks to ground then they would no longer sum and it would disconnect.

 

[telectrix]

Hi

If my electrical theory serves me correctly then a three phase RCD will not require a neutral because at any point in time the three phase voltages will sum to zero and therefore the currents. If one phase leaks to ground then they would no longer sum and it would disconnect.

correct, but the point is it feeds a 5 pin socket without a neutral incoming the RCD. any 5 pin 2P socket must have a neutral.

 

[Lucien Nunes]

If my electrical theory serves me correctly then a three phase RCD will not require a neutral

Only if the load does not have a neutral either. If it does, then the neutral must pass through the RCD, otherwise any neutral current produced by the load will be erroneously sensed as differential (leakage) current by the RCD.

at any point in time the three phase voltages will sum to zero and therefore the currents

That is only true if the impedances of the three load phases are identical. If they are different then the currents will differ even when the voltages are equal. But we're only interested in the line / neutral currents, which Kirchhoff's 1st law tells us must sum to zero in the absence of any leakage.

 

[UKPN]

Hi

If my electrical theory serves me correctly then a three phase RCD will not require a neutral because at any point in time the three phase voltages will sum to zero and therefore the currents. If one phase leaks to ground then they would no longer sum and it would disconnect.

As long as there is a path to return to the transformer
Regards UKPN

 

[Simon47]

I know of an outfit that sells/rents electric mini diggers. The machines only need 3P (no neutrals), but all their cables have 5 pin plugs/sockets - guess what they don't connect ? They could just as well use 4 pin plugs and sockets, and have some 5pin plug to 4 pin socket adapters in hand, but they didn't go down that route.
When I found this out I really really wanted to do something, but that would have caused major problems between my employer and client. At the time, they were sharing their 80+kVA diesel genny with our client while the power was off for pre-notified maintenance.
But at least I persuaded them to fit a c/o switch and inlet (as our client had just done) instead of using a widowmaker to power their unit when the mains was off.