RCD trips on new circuit

[thane]

I have installed a radial circuit but used 2.5 t&e on a 32a mcb, the circuit is just one double socket. My db is a split with a 80a rcd covering a 32a mcb for cooker and 2 32a rings, the other side has the 100a main breaker with 2 6a light circuits and a 16a immersion mcb.

I have verified no load on the cooker circuit and minimal on 1 of the socket circuits but the rcd still trips. it works with one of those plug in air freshners but not something larger such as a hoover or hammer drill.

i have replaced the cable and mcb but still nothing.

apologies if this has been covered before. thanks in advance for the help.

 

[EFLImpudence]

Have you put the neutral in the correct neutral bar i.e. the same one as all the other RCD protected MCBs?
Not sure about the freshener, do they use less than 30mA, anyone?

Also is the 32A MCB you have used for this radial the same as one of the ring circuits?

 

[Adam_151]

i. Which neutral bar bar did you put the circuit neutral in?
ii. What were your test results for the circuit?
iii. Why did you design your single socket radial cirucit as 2.5mm on 32A breaker... technically complies if you prove fault protection for the cable (until someone else tacks another socket on end!), but incrediably poor design practice!
iv. How are you handling the notification requires of the building regulations?

 

[flameport]

Not sure about the freshener, do they use less than 30mA, anyone?

They do, typically 3 or 4 watts, so between 13 and 17mA.

 

[JohnW2]

iii. Why did you design your single socket radial cirucit as 2.5mm on 32A breaker... technically complies if you prove fault protection for the cable (until someone else tacks another socket on end!), but incrediably poor design practice!

As EFLI has implied by his question, it could be that the new 'circuit' (2.5mm² cable supplying one socket) is actually a spur off one of the existing RFCs (originating at CU) - in which case it would presumably be perfectly acceptable design practice.

Kind Regards, John.

 

[thane]

Neutral is on the correct side and all reads are ok. i did the 5x also on both 0 and 180 degree all ok. the circuit layout is in anticipation for a future expansion of the circuit.

Thanks.

 

[securespark]

Sure??

 

[ban-all-sheds]

the circuit layout is in anticipation for a future expansion of the circuit.

So you plan to increase the load on the circuit?

What's the Iz of the cable?

 

[securespark]

Maybe he means the MCB is sized so the circuit can be extended into a RF circuit.

You could argue the difference between a 32A MCB feeding a single 2G socket via 2.5 cable and a 2.5 cable taken off a 32A MCB as a spur.

 

[Taylortwocities]

Untitled

• Taylortwocities
• 24 Jan 2010
• 4

 

[EFLImpudence]

Neutral is on the correct side

If that is so then either the cable is no good, but you say you have tried another, or you have wired the socket or connected the MCB incorrectly. Picture of inside CU?

and all reads are ok. i did the 5x also on both 0 and 180 degree all ok

You cannot find out why an RCD is tripping by making it trip.
Have you carried out an Insulation Resistance test?

the circuit layout is in anticipation for a future expansion of the circuit.

If you are going to have more than one socket on a radial circuit with 2.5mm² cable then you will have to fit a 20A MCB.

 

[JohnW2]

You could argue the difference between a 32A MCB feeding a single 2G socket via 2.5 cable and a 2.5 cable taken off a 32A MCB as a spur.

Indeed. As I implied in my previous post, I see no difference between having a 'radial circuit' consisting of 2.5mm² cable protected by a 32A MB supplying a single socket and having a 2.5mm² unfused spur (supplying one socket) from a 32A RFC.

Sure, someone could extend the radial circuit with more sockets, rendering it non-compliant and potentially dangerous - but exactly the same is true with an unfused spur on a 32A RFC.

If the neutral really is connected to the right place then, if what is happening is that the RCD is tripping whenever a load >30mA is put on the circuit, it almost sounds as if the N & CPC have been reversed - but it's seriously hard to think of how anyone could manage that! A N-E fault on the new circuit can't be the answer,because (assuming neutral connected to right bar!), that would result in loads on any of the RCD-protected circuits tripping the RCD.

I still suspect there's a simple explanation for what's happening, and I think a photo of the inside of this CU might reveal it!

Kind Regards

 

[sparkwright]

Have you checked the socket is wired correctly? Make sure the wires are not chaffed by the fixing screws, lugs, earth terminal. Does it trip with nothing plugged in?

 

[40 watt spark]

it almost sounds as if the N & CPC have been reversed - but it's seriously hard to think of how anyone could manage that!

I have actually seen this done.

The guy had replaced a DSSO faceplate with a different brand, and the terminal layout was different. He'd put the wires "in the same holes as they had been in on the old one" (no he didn't check the markings on the socket). He'd tested it with a plug in socket tester and of course got the 3 lights up, so it had to be OK.


Edited for Spellin

 

[sparkwright]

The Tenby sockets from the 80s look virtually identical to those of the 90s and 00s, but for some odd reason the L and N terminals are reversed.