RCD when no neutral

[Bacon]

Would there being any benefit in fitting a 63A 100ma RCD when you have no neutral to use with it?

 

[SPECIAL LOCATION]

How's it going to compare the line & neutral currents to identify an imbalance?

:|

 

[Bacon]

Well this is where the problem lies these rcd's are 3ph 63A 100ma for the purpose of charging fork lift trucks.

I told the client that not much purpose to having them fitted due to no neutral and told him test button will not fuction due to this as well.

But had to fit them any how as i was replacing nine in total on a like for like basis(9 x 3ph rcd's out)(9 new 3ph rcd's put back in) complete waste of time but i'm not paying for it.

 

[Sidewinder]

Bacon, were these the ones with an 80A mcb protecting the cct?

If so then there is an issue there.

 

[Bacon]

Yes sidey,In total their are 9 trucks each supplied via an 80A 3ph MCB to a 63A 100ma rcd then fly lead from socket to truck connection for charging purposes.

Now these have been in since the place was built so they are original items that were installed from day on.

I just can't understand why they were ever installed in such a way.

With out looking into one of the trucks i can't say how the charging takes place and what type of inverter may be present in them.

 

[Sidewinder]

Well even IF the rcd were wired to function correctly then it is overloaded really as it is only rated at 63A and "you" are allowing the circuit to run up to 80A.

The trucks probably have an inbuilt battery charger i would guess, so it could be balanced 3ph.

Though perhaps the earthing to the trucks should be verified?

 

[sellers]

'ang on a minuite!!

If you have a TP circuit the 3 phases should be balanced so when all 3 phases pass through the rcd there should be no EMF created on the coil inside, thus no trip. If you go to touch one of these phases current is lost which introduces emf inside the rcd activating the trip.

Same applies to 2 and 4 pole rcds. Don't forget on a 3phase + N supply the 3phase current total isn't the same as the neutral current. The best way I would explain it is that an RCD detects an imbalance on all line conductors.

 

[Bacon]

Thanks for that by the looks of them very similar the merlin gerin range of vigi MCB addon range.

 

[Andy™]

Well this is where the problem lies these rcd's are 3ph 63A 100ma for the purpose of charging fork lift trucks.I told the client that not much purpose to having them fitted due to no neutral and told him test button will not fuction due to this as well.

But had to fit them any how as i was replacing nine in total on a like for like basis(9 x 3ph rcd's out)(9 new 3ph rcd's put back in) complete waste of time but i'm not paying for it.

no offence, but are you sure your competent at this?

a TP RCD will work without neutral. if its a balanced load, there will be no neutral current anyway. you can get both 3 & 4 pole RCD's. you can use a 4 pole without a neutral. most have the test button wired accross 2 phases, but some phase - neutral. so whilst the RCD will still function, it wont trip with the test button (unless you add a similar resistance between neutral terminal and another phase)

 

[Sidewinder]

Andy,

Thinking about it IIRC the last time I fitted an MG 4P RCD there were instructions with it for use on 1p & N and 3P only with a resistor or summat.

My memory ain't what it used to be!

 

[Bacon]

[quote name='Andy

 

[Sidewinder]

Bacon,

I think that your situation depends on more things than we know mate.

 

[Andy™]

how are the FLT's conencted?

most FLT chargers ive dealt with are plugged/hard wired to supply, and connected to FLT via anderson conectors. and there usually 20A supplies max

 

[Bacon]

Trucks are connected as follows,

Mains supply fed to 63A 100ma rcd Surface mount combined unit, angled socket

fly lead plug and socket to housing on truck,

Thas it Andy 9 in total all with own supply to each surface mount combined unit.

Thanks

 

[Sidewinder]

Bacon,

I guess you mean the 3ph red commando socket units?

IF so what is the socket rating, as the mcb must be less than or equal to this?

 

[Bacon]

Commando socket units

socket ratings are 63A Sidey.

 

[Andy™]

as SW says, commando sockets must have overload at or lower than their rating, except 16a (can be protected by 20A)

 

[Sidewinder]

In that case mate, EDN immediately for overloading.

Really you should not have worked on the cct as it is dangerous.

 

[Bacon]

Thanks for all the advice will get it sorted out Monday hopefully.

 

[steptoe]

[quote name='Andy