Rcd tripping on new hot tub circuit

[Thorfinn skålsplitr]

I'm having a problem with the CU rcd tripping out, I have installed a feed outside to my daughters hot tub using 6mm cable about 14mts in length going to a metal clad dis board and from there via a 32A mcb to a 32A switched socket, insulation is good, no damp, but when I connected up the tub the rcd tripped, I removed the connections and connected a socket to connect a kettle as a test load everytime the kettle was turned on the rcd tripped, Ideas please tia

 

[James]

What are the trip times for the rcd?

have you done a ramp test with no loads connected?

 

[telectrix]

incorrect wiring. N-E reversed or N in wrong bar. are my thoughts.

 

[Thorfinn skålsplitr]

What are the trip times for the rcd?

have you done a ramp test with no loads connected?

No, I didn't think about that I shall have to dig out my test meter, as soon as I've done as you've suggested I will post, thanks

 

[Thorfinn skålsplitr]

No, I didn't think about that I shall have to dig out my test meter, as soon as I've done as you've suggested I will post, thanks

One thing, the rcd is fine as long as this particular circuit is not used

 

[Thorfinn skålsplitr]

What are the trip times for the rcd?

have you done a ramp test with no loads connected?

T1 1999ms
T2 1999ms
T3 45ms
T4 42ms
T5 26ms
T6 16ms
I don't have facilities to do a ramp test

 

[DPG]

No, I didn't think about that I shall have to dig out my test meter, as soon as I've done as you've suggested I will post, thanks

Normal practice would be to have your tester out beforehand so that you can test the new circuit!

 

[Thorfinn skålsplitr]

Normal practice would be to have your tester out beforehand so that you can test the new circuit!

I know but the cable and fittings are all brand new just tested with the meter and all is sound. Run a new 6mm cable to test(after testing said cable) from the CU to hot tub and it still trips the rcd, I'm stumped at the moment

 

[pc1966]

Is it a single 30mA RCD for the whole house?

A bit more detail would help. It might be just the leakage of the tub is accumulating too much for the RCD. Do you have a clamp ammeter (that can measure down to mA) you could check the leakage with by clamping both tails?

 

[Thorfinn skålsplitr]

incorrect wiring. N-E reversed or N in wrong bar. are my thoughts.

I run a separate 6mm test cable from CU to tub, cutting out the outside dis board and switched socket to see if it would stay in but it still tripped

 

[Thorfinn skålsplitr]

I run a separate 6mm test cable from CU to tub, cutting out the outside dis board and switched socket to see if it would stay in but it still tripped

Cables, dis board and switched socket and cable end are all correctly connected it was the first thing I checked

 

[Thorfinn skålsplitr]

Is it a single 30mA RCD for the whole house?

A bit more detail would help. It might be just the leakage of the tub is accumulating too much for the RCD. Do you have a clamp ammeter (that can measure down to mA) you could check the leakage with by clamping both tails?

Yes just a single 30 mA rcd, besides can't get it to stay on long enough to test

 

[pc1966]

It could be a fault in the hot tub, given it holds out on a kettle. Can you IR test the tub at 250V (just in case electronically switched) to check that L+N to E is showing tens of Mohm?

Another possibility is a N-E short somewhere (not necessarily on the new circuit). If you are on a TN-C-S supply the origin N-E voltage is practically zero so typically that only shows up if you have loads of tens of amps or more. It might be the kettle at ~10A is not enough to cause enough N-E current to divert, but the tub coming on pump and heaters at 30A (or more, if motor surge is simultaneous, etc) is enough to reach threshold.

 

[pc1966]

If you suspect a N-E short then switch off the main supply (so both L & N isolated at the origin) and do a global IR taking L+N to E, maybe at some convenient socket (having made sure RCD reset and socket switched on!).

Again 250V is safer to play with, but L+N to E should always be safe to test at 500V (unlike L-N on low power electronics where 250V is max to try just in case).

 

[Thorfinn skålsplitr]

It could be a fault in the hot tub, given it holds out on a kettle. Can you IR test the tub at 250V (just in case electronically switched) to check that L+N to E is showing tens of Mohm?

Another possibility is a N-E short somewhere (not necessarily on the new circuit). If you are on a TN-C-S supply the origin N-E voltage is practically zero so typically that only shows up if you have loads of tens of amps or more. It might be the kettle at ~10A is not enough to cause enough N-E current to divert, but the tub coming on pump and heaters at 30A (or more, if motor surge is simultaneous, etc) is enough to reach threshold.

It trips on the kettle as well and that is 3kW

 

[Thorfinn skålsplitr]

It trips on the kettle as well and that is 3kW

The insulation test is 400 megohms plus

 

[pc1966]

It trips on the kettle as well and that is 3kW

Ah, sorry misread that.

I would look again at the new cable at the CU end as @telectrix said to be very sure the N is in the correct neutral bar (post-RCD, not supply N).

 

[MJPD29]

Scary that you wouldn't get an electrician to test the circuit but youll let your daughter sit in a giant kettle that you DIY wired

 

[Thorfinn skålsplitr]

Ah, sorry misread that.

I would look again at the new cable at the CU end as @telectrix said to be very sure the N is in the correct neutral bar (post-RCD, not supply N).

Thanks, the neutral was connected to the supply N so I'll check that out tomorrow. 415-11kV is my forte seems your never too old to learn...

 

[telectrix]

could it be a N-E fault on a completely different circuit, so that when a large load is applied on the new circuit, the RCD sees imbalance . had it before where a N-E fault in a shower switch tripped the RCD that fed the other half of a dual RCD board. time for an electrician methinks.