Square D Cut Out Query.

[Formaleins]

I hope someone might have an idea as what is going on here. I have a Square D Consumer Unit fitted with a Schneider RCBO on the mains coming in and then circuit breakers for all the outputs. There is one 45A breaker that is only connected to my Panasonic Multi Point Heater.

I was doing some checking today on the thermos cut outs on the shower so I tripped the breaker for that circuit.

 

Luckily I didn't jump in and just on caution checked the supply to the heater. I was surprised to find that even with the trip open on the consumer unit, the shower still had 35V / AC on the inputs. Has anyone any idea as to where to start hunting down the problem? As I say, the heater is on its own ring with nothing else connected just the live neutral and earth.

 

It has to be something leaking from Neutral somewhere do you think?

 

Any ideas would be useful thanks.

 

[Crossy]

Did you measure with a DMM? It's probably just capacitive pickup from other live circuits. If you use a regular analog meter it should go away.

 

If you have damp hands and are very sensitive you may feel a tingle, but it's not harmful other than making you jump and spill your tea (and burning yourself).

 

[Formaleins]

Just now, Crossy said:

Did you measure with a DMM? It's probably just capacitive pickup from other live circuits. If you use a regular analog meter it should go away.

 

If you have damp hands and are very sensitive you may feel a tingle, but it's not harmful other than making you jump and spill your tea (and burning yourself).

 

Many thanks again for that Crossy! Hopefully that is the case and yes I was using a Fluke 17B DVM. Unusual though as I have never noticed it before, then again I hadn't really been looking. Good to know it isn't trying to kill me.

 

Thanks for your help. (I'll ask the wife to touch it to check, tell her it's for good luck)

[sometimewoodworker]

4 hours ago, Formaleins said:

There is one 45A breaker that is only connected to my Panasonic Multi Point Heater.

That sounds a little extreme for a single appliance. Do you have 16mm² or at least 10mm² cables feeding the water heater?

[Formaleins]

6 minutes ago, sometimewoodworker said:

That sounds a little extreme for a single appliance. Do you have 16mm² or at least 10mm² cables feeding the water heater?

It is 6mm cable, running max of about 34Amps. on an 8kW heater, the run is no more than about 8 metres so it is not too bad. The breaker probably should be changed to a lower one but it has 4 trip points from consumer unit to the actual heater and has never had any problem. (The original "Spark" had wired it with 2.5mm and the original heater was a 10KW jobby!)

[bankruatsteve]

55 minutes ago, Formaleins said:

 but it has 4 trip points from consumer unit to the actual heater and has never had any problem. 

What are you calling trip points?

 

Although the breaker is over sized, it will not be an issue given the single load.

[sometimewoodworker]

2 hours ago, Formaleins said:

It is 6mm cable, running max of about 34Amps. on an 8kW heater, the run is no more than about 8 metres so it is not too bad. The breaker probably should be changed to a lower one but it has 4 trip points from consumer unit to the actual heater and has never had any problem. (The original "Spark" had wired it with 2.5mm and the original heater was a 10KW jobby!)

Since the breaker is there to protect the cable it is significantly too big. Your 34Amps load maximum will work perfectly well on 32A breaker (the recommendation for 6mm² cable) as a slight over amperage will not trip it within for a long time if at all. Also it’s quite likely that the heater seldom if ever actually draws the maximum available.

[Formaleins]

2 hours ago, sometimewoodworker said:

Since the breaker is there to protect the cable it is significantly too big. Your 34Amps load maximum will work perfectly well on 32A breaker (the recommendation for 6mm² cable) as a slight over amperage will not trip it within for a long time if at all. Also it’s quite likely that the heater seldom if ever actually draws the maximum available.

I like to leave a bit of leeway as some of the voltages and current spikes and dips are often extreme around here and the Schneider RCBO trips if a fly puts its wings between live and neutral. ( I think I need nearer 34 Amps on this circuit) Besides, 22 years ago when we were building the place, all we had was a chunk of soldered copper on a breaker fuse that was supposed to melt when it reached 60 Amps, you would be charcoal before that thing melted. So safety has improved a lot since those days. There was hardly a day went buy that the news was not reporting someone electrocuted by simply walking down the street when it was a little bit humid. I recall one time fiddling about at the main breaker when we were setting up the electric supply, we were using the cheapo 5 Amp "Agricultural" meter, I forget what I was doing but I do not forget the result, I got the full 5/15 Amps into my teeth. If you have fillings and have bit onto a piece of tin foil, multiply that by 10,000 and you will get an idea of the force, and it didn't trip didly squat! I was only concerned about having 35 Volts showing on my shower inputs with the breaker open. Nothing else is a problem, my cut outs cut out pretty damn quick, I have had plenty of experience each time I make a mistake!

[tjo o tjim]

You might also want to check voltage across the breaker (line-load) to make sure you don’t have a high impedance connection with the breaker open. Much more likely that it is just leakage as crossy states, but if it is an older unit good to confirm. 

[sometimewoodworker]

22 minutes ago, Formaleins said:

like to leave a bit of leeway as some of the voltages and current spikes and dips are often extreme around here and the Schneider RCBO trips if a fly puts its wings between live and neutral.

You seem to be missing the point that the breaker is there to protect the cable. So by oversizing the breaker you are defeating that protection. Your 45Amp breaker is almost certainly going to happily pass 55Amps for hours and if you’ve got that much fault current flowing the 6mm cable is going to get quite toasty.

 

If you are having that much variation then putting in under over regulation, easy and not expensive, would be a very good idea. 
 

[Formaleins]

42 minutes ago, sometimewoodworker said:

You seem to be missing the point that the breaker is there to protect the cable. So by oversizing the breaker you are defeating that protection. Your 45Amp breaker is almost certainly going to happily pass 55Amps for hours and if you’ve got that much fault current flowing the 6mm cable is going to get quite toasty.

 

If you are having that much variation then putting in under over regulation, easy and not expensive, would be a very good idea. 
 

You cannot compensate for stupidity. The idiots around here mess with the supply with huge welders and other juice suckers, sometimes my supply will drop to 120 Volts. Usually an idiot in the village messing with the supply. I can only hope that each time it drops below 200V one of them is getting fried. I read recently that one of the local intellectuals was found dead in a well after riding his pushbike into it at 3 Am, Darwinism in action. 6MM Cable is (or was fine) for short runs up to about 9.2KW. The regs. were changed not too long back now specifying 10mm. Yes, 10mm would be better to future proof, but for my application it isn't an issue and no, the cable does not even get warm. it is 70C rated and well within the 54 A spec. The more worrying problem is when they mess with the supply further up the village we end up getting about 150 Volts and then the water pump goes mental. It cannot push the water through and just runs and runs until it runs dry then the thermal cut outs come in. This has to be damaging it, but there is no comeback on these idiots. The other thing is if you have PC's, the sods can disrupt the supply for about 2 seconds and cause the PC's to reboot... they have crashed my PC's over and over, again, you cannot get justice and go out and hang them. (Sadly)

[Formaleins]

Funny but every topic you post here these days (which is why I no longer bother posting , reading or responding) ends up with some smart <deleted> doing a "Spanish Inquisition" and a tear down of the original post.

I ask about why I have 35 Volts on my heater when the Breaker is off, and it ends up with an inquisition into the diameter of my cables, the cable length, the type of breakers...have these people nothing better to do?

 

<deleted> it! Another notch in the tree of <deleted> responses and another reason not to bother posting to this site anymore. Thanks for the help Crossy but these <deleted> really are too much to bear!

[sometimewoodworker]

15 hours ago, sometimewoodworker said:

You seem to be missing the point that the breaker is there to protect the cable. So by oversizing the breaker you are defeating that protection. Your 45Amp breaker is almost certainly going to happily pass 55Amps for hours and if you’ve got that much fault current flowing the 6mm cable is going to get quite toasty.

My mistake 

The  cable is rated for single conductors at 48 amps in free air