15A/45A Electric supply Single Phase getting HOT!

[menzies233]

I was wondering if my water heater is actually suitable to use here in Thailand. It is a Panasonic 10kW Multipoint. It has three power levels, 3kW, 6kW and 10kW. The local supply here is a bit iffy, we tend to suffer from voltage drops going down to 190V depending how many people are using power on our transmission line, despite being the first consumer taking the juice from the step down transformer mounted on the pole where our meter is located.

At 3kW the water this time of year is just lukewarm taking a shower, pretty chilly here in the North this time of year in the mornings. 6kW can be OK, but it tends to fluctuate quite a bit depending on the voltage, i.e. it tends to go hot and cold a bit. I tried the 3rd Setting 10kW and there was a terrible stink of electrical insulation melting, I checked the main cable into the Safety Cut and it was almost glowing, and had started to melt the plastic insulation.

We are using the heavy multicore aluminium cable on a run of about 80 metres from the meter, the cable is about 1cm in diameter, pretty heavy duty.

Am I asking too much taking 10kW? I guess it is close to the 45Amp limit of the meter, but why would the cable have a problem? All the connections are extremely tight, the cable I believe is rated at 750V, is it just too much to handle?

Cheers.

[metisdead]

Moving to the Electrical forum.

[bankruatsteve]

Hmmm. A 1cm diameter cable would be 78.5mm2 cross section area - and that certainly sounds heavy duty. 80m is a bit of a stretch though and too lazy to look up R value for Al on that length. What else was running with the shower? It's obviously overloaded if melting stuff. Wait for Crossy. He'll know.

[menzies233]

Hmmm. A 1cm diameter cable would be 78.5mm2 cross section area - and that certainly sounds heavy duty. 80m is a bit of a stretch though and too lazy to look up R value for Al on that length. What else was running with the shower? It's obviously overloaded if melting stuff. Wait for Crossy. He'll know.

It is an approximation of diameter, it is pretty thick, quite heavy aluminium, the largest gauge used around here, not the blue PVC stuff, there was nothing else running when the shower was on, only the water pump to feed the shower.

I was surprised the cable coating melted / burned, rather than some cut out or damage to the meter. (I used to have the 5/15A Meter and we were charged for frying that one) I guess 10kW is close to the load of the meter but as for the cable????? (It is heavy duty stuff from Bangkok Cable, not cheap junk)

I was worried about the screws on the Safety-Cut, not being able to handle the current but you would think the screws would fry rather than the PVC sheath melting.

[GuestHouse]

The dimention that matters is the cross sectional area of each conductor (live AND neutral)

Do you have any idea what the size of theses conducting cores is?

How is the cable installed, in open air, burried in the ground or in a conduit?

If you have used a cable that is not designed for direct burrial or constant exposure to moisture then mosture damage to the insulation msy be a problem.

Are the cable conductors the same size? (ie has the electrician wired either the live or nuetral to and undersizes core)?

Did you buy a duff cable? - I suggest getting a different electrician to check the cable for you.

Get him to check the following:

Cable core sizes (both live and neutral)

Megga test the cable (burned sheathing suggests you need to change the cable)

Resistance of the cable run (connect the conductors together at one end and check the resistance from the other end.

---

My best guess is that if each conductor is 12mm square or bigger then your cable sheath is damaged or you have an uneven core cross section somewhere in the circuit.

But I would also check to make sure both live and neutral cores are the same cross sectional area.

Two last dumb points - Has the electrician left any coils of cable in the circuit?

Has a neighbour tapped into your meter or somewhere along the 80 metrers?

[Lampang2]

Things also needs to be tightened. (hard)

No loose connections.

[Crossy]

The cable should be marked along its length with the size and type, that's what we need to know.

10kW @ 220V is 45A, on the line for the 15/45, but even a 10mm² Al cable should not be getting hot enough to smoke.

Serious investigation needed, could even reveal the cause of your low voltage.

Also as above, check the incoming connections to the Safe-T-Cut (care! the supply will still be live), Al cable has a nasty habit of work-flowing away from pressure points resulting in loose connections.

As I noted, first thing is to find the actual cable size.

[menzies233]

The cable should be marked along its length with the size and type, that's what we need to know.

10kW @ 220V is 45A, on the line for the 15/45, but even a 10mm² Al cable should not be getting hot enough to smoke.

Serious investigation needed, could even reveal the cause of your low voltage.

Also as above, check the incoming connections to the Safe-T-Cut (care! the supply will still be live), Al cable has a nasty habit of work-flowing away from pressure points resulting in loose connections.

As I noted, first thing is to find the actual cable size.

I think the cable originally had "Bangkok" cable or similar, however the UV has taken its toll and I can find nothing on it now. The cable is made up of 7 aluminium cores which appear to be just over 1mm diameter per core. The total diameter of the cable and insulation is about 8mm, I have been told by two electricians (Not Thais) that it is fine.

The cable began melting at the entry to the Safe-T-Cut, no where else, about 1 inch from the screw connectors which made me suspect a poor connection, however everything seems rock solid.

Thanks for the help!

[menzies233]

The dimention that matters is the cross sectional area of each conductor (live AND neutral)

Do you have any idea what the size of theses conducting cores is?

How is the cable installed, in open air, burried in the ground or in a conduit?

If you have used a cable that is not designed for direct burrial or constant exposure to moisture then mosture damage to the insulation msy be a problem.

Are the cable conductors the same size? (ie has the electrician wired either the live or nuetral to and undersizes core)?

Did you buy a duff cable? - I suggest getting a different electrician to check the cable for you.

Get him to check the following:

Cable core sizes (both live and neutral)

Megga test the cable (burned sheathing suggests you need to change the cable)

Resistance of the cable run (connect the conductors together at one end and check the resistance from the other end.

---

My best guess is that if each conductor is 12mm square or bigger then your cable sheath is damaged or you have an uneven core cross section somewhere in the circuit.

But I would also check to make sure both live and neutral cores are the same cross sectional area.

Two last dumb points - Has the electrician left any coils of cable in the circuit?

Has a neighbour tapped into your meter or somewhere along the 80 metrers?

Cable is open air, both live and neutral are exactly the same sizes, no one is tapping off, there are no coils of excess cable, just a straight run to the meter. There were a couple of points where the outer insulation was worn where it was originally fitted to the old posts, but these are only small and have been taped up just in case. As I said in a post to Crossy, it just begins melting at the entry to the Safe-T-Cut, about an inch or so out from the screws. The main cable is not even warm if you get about 10 yards out.

[Robroona]

Loose or dirty connection is my suggestion.

[bankruatsteve]

Has the cable been trimmed to fit the Safe-T-Cut?

[Crossy]

Al with an overall diameter of about 8mm will be THW-A 16mm² rated at 69A in air http://www.bangkokcable.com/product/backoffice/file_upload/140522_750V70C_THW-A_LV.pdf

Should be fine on a 15/45, possibly a volt-drop issue if the run is long, but that won't cause the stated problem.

From what is described I still think it's a loose connection fizzing under load, take everything apart, clean up and re-make all the connections. A connection that's been overheated may feel fine, but still be high resistance.

NOTE Do not attempt this yourself, get a local sparks to fix it for you, if he does it live and fries himself it's not you.

[GuestHouse]

Agree with Crossy, if the insulation is melting near a termination it is likely to be a loose or dirty connection.

Get an electrician to disconnect, inspect, clean and remake the connections.

If there is sufficient spare length, recut the cable to remove the overheated section before reconnecting.

If the cable cores are stranded wires get the electrician to fit compression cable crimps on the cable - make sure he uses the correct tool to ensure correct crimping.

[menzies233]

Agree with Crossy, if the insulation is melting near a termination it is likely to be a loose or dirty connection.

Get an electrician to disconnect, inspect, clean and remake the connections.

If there is sufficient spare length, recut the cable to remove the overheated section before reconnecting.

If the cable cores are stranded wires get the electrician to fit compression cable crimps on the cable - make sure he uses the correct tool to ensure correct crimping.

I had some left over cable that I cut a section from today and to be honest, I do not think it is Bangkok cable after all, the aluminium conductors look fine but the insulation is not exactly what you would want. It varies in thickness from about 0.5mm to about 0.2mm - and consistently, although the cable appears round, the insulation is oval so it is possible it is a crap cable. The connections are all clean and tight, I have checked and cleaned and retightened already, plenty of clean metal connection to the Safe-T-Cut. Thanks for the suggestions but it looks like I might go and buy a new cable. (I could have swore it was Bangkok cable but I am obviously mistaken).

Cheers.

[Crossy]

With insulation that thin I would want to replace it.

How long is your run from the meter?

Are you intending using copper or more Al?

[Pacificperson]

Did you clean the safe-T-cut side of the connection? Checking only the cable may not solve the problem.

[bankruatsteve]

Get some of the anti-oxidant gell that should be available at places that sell cable and apply to the exposed areas of the Al. It's possible if there was any trimming or damage to the cable that left little spikes they would easily arc even with a tight connection.

[GuestHouse]

It seems very clear you have an electricution, burn and possibly fire risk.

Replace the cable before the worst happens.

[menzies233]

With insulation that thin I would want to replace it.

How long is your run from the meter?

Are you intending using copper or more Al?

The run from the meter is about 80 metres, the thickness of the insulation obviously has no bearing on the current capacity of the cable as air is not a bad insulator, I just make sure I check it before I touch it. If I replace it it is going to be Al. not Cu as the copper is a hell of an expense, and having been here a few years and bought brass brushes etc. you are more likely to get plated junk.

[menzies233]

It seems very clear you have an electricution, burn and possibly fire risk.

Replace the cable before the worst happens.

Agree, I think the insulation is rubbish, and the cable may be suspect, but it is still a size that should handle a reasonable current. maybe it is just junk, it just seems strange that it starts melting about 1 or 2 inches from the 60Amp Safe-T-Cut connection, the rest of the cable does not even get warm.

Checked it at the meter end and it is barely warm, I am wondering if a 10KW Heater is asking too much? as it must be pulling 40 Amperes or more. None of the trips trip, and the Safe-T-Cut stays on, maybe our supply is not up to it? There are a few signs that would indicate not enough juice getting to the house, put on the shower at 6KW and the fans all slow down to half speed, you cannot fire up a fluorescent light, so something is not getting enough oomph.

[Crossy]

We have suggested the most likely reason, if that's not it we need to see the problem could be a faulty batch of cable.

Please post photos of the damaged area and the connection at the Safe-T-Cut.

Also, 80m of 16mm² Al at 50A is going to give you a significant volt drop (about 8%) on top of any drop already there at the meter. If replacing the cable go bigger, in Al I'd suggest 35mm² (25 in Cu). Calculator here http://www.doncastercables.com/technical-help/ result is for Copper, go one size bigger in Aluminium.

Do you have a multimeter (cheap) to check your actual supply voltage?