Sun heat on caravan cable causing meter box circuit breaker to pop?

[TimGemm]

Could the sun’s heat on a caravan mains supply cable cause the fuse/circuit breaker at the meter box/supply end to trip?

 

[James]

Not if the cable is in sound condition.

 

[littlespark]

Are we talking New Zealand sun here?

It should be a specific cable for outdoor use.
Some domestic types, designed to be used in homes and buried in the fabric of the building will react to UV light over time, the plastic hardens and cracks.

The other issue could be overload. What size is the breaker, size of cable, load in caravan and distance between breaker and caravan.

Circuit breakers can also become weak over time… and will just trip for no reason.
From what I know of New Zealand electrics, is the meter box outside and maybe open to the elements? Has water got in somewhere?

 

[Rockingit]

Could the sun’s heat on a caravan mains supply cable cause the fuse/circuit breaker at the meter box/supply end to trip?

I'd say it's unlikely but not impossible. There are two parts to a standard breaker - a magnetic component that trips it really quickly in the event of a fault and then a thermal bi-metallic strip that reacts over time to deal with the creeping up of heat caused if you're overloading the circuit. The standard reference temperature for a normal breaker is 30℃ however the load capacity decreases by 6% for every +10℃ increment - so if for arguments sake your breaker is in a tin box on the roof with the sun beating down and roasting it, in addition to the heat transfer from a cable doing the same then your figures are going to drop pretty quickly.

Only you know how hot is hot and what loads are happening - if it only happens at midday with full aircon running then that should guide you as to where to look!!

 

[TimGemm]

Not if the cable is in sound condition.

Thanks James. I think there must be a fault in the circuit breaker box that sits inside the meter box. Three times in the last 10 days, the circuit breaker for the caravan/tiny house has tripped in the meter box (never in the cabin’s fuse board) always early afternoon. And it keeps tripping, even with cabin mains Off. And then next morning (yesterday it was at 10pm) it works again.

 

[James]

Thanks James. I think there must be a fault in the circuit breaker box that sits inside the meter box. Three times in the last 10 days, the circuit breaker for the caravan/tiny house has tripped in the meter box (never in the cabin’s fuse board) always early afternoon. And it keeps tripping, even with cabin mains Off. And then next morning (yesterday it was at 10pm) it works again.

check out @Rockingit post above, there is some good advice there.
heat may be a factor if the breaker is getting hot.

alternatively, some strange fault where the cable expands when it gets hot and a damaged piece comes into contact with earth.
my above suggestion is far far less likely than the post above, just there to point out that every 10,000 strange faults you come across, one or two have the weirdest cause that you would never have thought about.

first rule out the normal
then the abnormal
then the strange and unusual

finally if none of the above have found it then you are in the weird world of the 1 in 10,000 where we have to check that at, if from 12.00 to 14.00 when the heat is at its highest, a group of local snails doesn't come in to hide from the heat and short out a breaker before falling out of sight behind the post!!

 

[TimGemm]

I'd say it's unlikely but not impossible. There are two parts to a standard breaker - a magnetic component that trips it really quickly in the event of a fault and then a thermal bi-metallic strip that reacts over time to deal with the creeping up of heat caused if you're overloading the circuit. The standard reference temperature for a normal breaker is 30℃ however the load capacity decreases by 6% for every +10℃ increment - so if for arguments sake your breaker is in a tin box on the roof with the sun beating down and roasting it, in addition to the heat transfer from a cable doing the same then your figures are going to drop pretty quickly.

Only you know how hot is hot and what loads are happening - if it only happens at midday with full aircon running then that should guide you as to where to look!!

Thanks for that. The circuit breaker is in a shady spot so I don’t think it is getting hot. The cable is mostly in the sun so it heats up a bit.
Initially I thought the fault was the caravan plug ends, which water had entered over time and caused some corrosion of the earth connection. I have replaced these plug ends, and I noticed that the earth wire copper is a bit darker coloured than the bright fresh copper colour of the other 2 wires.
Only load when circuit trips is a stereo and a fridge and a charging phone. Cheers

 

[James]

I think i would be inclined to replace the circuit breaker with a new one of the same specification and see if the problem goes away.
it is a cheep fix / test.
if that doesn't work then it is down to some serious testing.
Insulation resistance would be a good place to start, if that shows no faults then perhaps a current logger to check that no unknown loads apear when the sun is up, an unknown ventilation fan on a thermostat? or it may show a sudden increase to max scale showing a short circuit is more likely.
sounds like it is not an easy one to find. (this fault)

 

[TimGemm]

I think i would be inclined to replace the circuit breaker with a new one of the same specification and see if the problem goes away.
it is a cheep fix / test.
if that doesn't work then it is down to some serious testing.
Insulation resistance would be a good place to start, if that shows no faults then perhaps a current logger to check that no unknown loads apear when the sun is up, an unknown ventilation fan on a thermostat? or it may show a sudden increase to max scale showing a short circuit is more likely.
sounds like it is not an easy one to find. (this fault)

Ok thanks, I’ll try the circuit breaker. It’s just tripped again right now. Cloudy day, 21degrees so it wasn’t a sun-heated cable this time. I did have the oven, induction hob(on low), stereo, fridge and battery charger all going however…..

 

[Rockingit]

Ok thanks, I’ll try the circuit breaker. It’s just tripped again right now. Cloudy day, 21degrees so it wasn’t a sun-heated cable this time. I did have the oven, induction hob(on low), stereo, fridge and battery charger all going however…..

Can you define what type of breaker it is, please? A picture will help.

 

[TimGemm]

Are we talking New Zealand sun here?

It should be a specific cable for outdoor use.
Some domestic types, designed to be used in homes and buried in the fabric of the building will react to UV light over time, the plastic hardens and cracks.

The other issue could be overload. What size is the breaker, size of cable, load in caravan and distance between breaker and caravan.

Circuit breakers can also become weak over time… and will just trip for no reason.
From what I know of New Zealand electrics, is the meter box outside and maybe open to the elements? Has water got in somewhere?

Thanks for the

Are we talking New Zealand sun here?

It should be a specific cable for outdoor use.
Some domestic types, designed to be used in homes and buried in the fabric of the building will react to UV light over time, the plastic hardens and cracks.

The other issue could be overload. What size is the breaker, size of cable, load in caravan and distance between breaker and caravan.

Circuit breakers can also become weak over time… and will just trip for no reason.
From what I know of New Zealand electrics, is the meter box outside and maybe open to the elements? Has water got in somewhere?

thanks for that. Yeah it’s NZ but it is super durable outdoor cable. No sign of any damage or deterioration. It’s 6mm2 as it’s 100m long. It has worked perfectly for 3 years. Meter box is outside but no evidence of any water getting in. The caravan cable plug ends (those big blue ones) did get water in and caused some corrosion of the earth wire connection but I have replaced the plugs. I did notice that the copper of the earth wire is a bit darker than the other two wires, which still look like brand new copper. Maybe the earth wire isn’t performing to full capacity? But most of the time it works fine.
Could well be the circuit breaker becoming weak as you suggest. The weird pattern that is happening is the circuit breaker for the caravan plug trips around lunchtime and won’t reset, so I leave it and try again in the evening (8 or 9pm) and it works. This has happened 3 times in 10 days .

 

[Rockingit]

That breaker is actually an RCBO which means it’s a combined ‘fuse’ as well as an earth leakage device (what the yanks call a GFDI) so your fault might actually be as simple as a defective appliance

 

[TimGemm]

That breaker is actually an RCBO which means it’s a combined ‘fuse’ as well as an earth leakage device (what the yanks call a GFDI) so your fault might actually be as simple as a defective appliance

Ok thanks ! Each time when that orange switch trips, I go to the cabin and turn the mains Off (supply into cabin). Then I try reset the orange switch in the meter box, but it keeps tripping. I leave if for 8-12 hrs and then it works. Does this suggest it’s either the circuit breaker or the cable? I have no idea what changes in the 8-12hrs so that it works……

 

[Rockingit]

Ok thanks ! Each time when that orange switch trips, I go to the cabin and turn the mains Off (supply into cabin). Then I try reset the orange switch in the meter box, but it keeps tripping. I leave if for 8-12 hrs and then it works. Does this suggest it’s either the circuit breaker or the cable? I have no idea what changes in the 8-12hrs so that it works……

An electrician with the right test gear could pin point this within a couple of hours. I’m over your way in March / April but sadly don’t have an NZ license else I’d offer to help!

 

[littlespark]

My wife’s over there just now visiting her brother….

Do NZ sparks have test equipment like UK, or do they follow the bang test method?

 

[Rockingit]

Ok thanks ! Each time when that orange switch trips, I go to the cabin and turn the mains Off (supply into cabin). Then I try reset the orange switch in the meter box, but it keeps tripping. I leave if for 8-12 hrs and then it works. Does this suggest it’s either the circuit breaker or the cable? I have no idea what changes in the 8-12hrs so that it works……

That sounds more like a cable issue causing the RCD to trip - are there any joins anywhere where water or damage could have happened?

 

[Rockingit]

That sounds more like a cable issue causing the RCD to trip - are there any joins anywhere where water or damage could have happened?

Or the other way around - are there any ‘wet’ appliances such as a washing machine inside the cabin which could be taking that amount of time to dry out a fault? It’s feasible that if still plugged in but ‘off’ if you only have single pole isolation that it could upset an RCD. You’ll have to physically unplug every single last item from the wall next time it happens and see if the recovery time improves.

 

[TimGemm]

That sounds more like a cable issue causing the RCD to trip - are there any joins anywhere where water or damage could have happened?

Ok thanks. There are no joins or external damage but the plugs at both ends of the cable let some water in over time. There was corrosion inside the plugs particularly where the earth wire joins the plug. I have replaced the plugs, but I did notice that the earth wire copper core is now a darker colour of copper than the bright fresh looking copper colour of the other two wires. I cut a foot or so off each end to get rid of the worst of the earth cable, but the copper core is still a bit darker than the other two cores.

 

[Rockingit]

Ok thanks. There are no joins or external damage but the plugs at both ends of the cable let some water in over time. There was corrosion inside the plugs particularly where the earth wire joins the plug. I have replaced the plugs, but I did notice that the earth wire copper core is now a darker colour of copper than the bright fresh looking copper colour of the other two wires. I cut a foot or so off each end to get rid of the worst of the earth cable, but the copper core is still a bit darker than the other two cores.

Whilst it can also be caused by normal corrosion, what you describe instantly red flags with me as a heat/overload situation. If there has been current passing to the earth (in the U.K. we call that the CPC) then obviously that will generate heat - except if the terminals haven’t been done properly (eg aren’t tight enough) then you can end up with some arcing which is normally where that discolouration in the copper comes from.

 

[brianmoooore]

Whilst it can also be caused by normal corrosion, what you describe instantly red flags with me as a heat/overload situation. If there has been current passing to the earth (in the U.K. we call that the CPC) then obviously that will generate heat - except if the terminals haven’t been done properly (eg aren’t tight enough) then you can end up with some arcing which is normally where that discolouration in the copper comes from.

Not sure I agree, especially if it's the CPC that's deteriorated. The corrosion described sounds like that which is quite common on automotive cables. You find a damaged cable, find the blackened copper which wont solder, and have to strip back some distance to find reasonably bright solder that you can make a reliable splice to.