Replacement electric hot water element question

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Technofreak

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#273049 1-Aug-2020 14:01

The element on our hot water cylinder died late yesterday. While I was draining the cylinder I went out this morning and bought a new 3kw element based on the size of the cylinder. It measures up at about 135 litres. Now that I have the old element out I see that it is a 1.5 kw element.

Will the wiring be ample for a 3kw element? The house is a mid 1970's house. I see from a copy of NZECP 51:2004 that water heater wiring for up to 3kw heaters is supposed to be 1.5 mm sqr. My guess is I should be OK. The wiring is three strands of about 0.9mm diameter which I've roughly calculated to be 2 mm sqr.

One thing that has made me doubtful about the circuit capacity is the fuse label. The fuse has 5 amps embossed on the ceramic case, however it's anyone's guess what size wire is fitted. 5 amps isn't really sufficient for 1.5 kw so I'm suspicious someone in the past has used a 5 amp holder and put in heavier fuse wire.

A 3kw element will need a 15 amp fuse.

I'm prepared to go back and swap the element but the only smaller size element I can get today is 2kW which isn't a big stretch on 1.5 kw. However if the 3kw will be OK I'll stick with that.

I'd appreciate thoughts, feedback from those with expertise on this.

Thank you.

Like most other things about this place I suspect the previous owner just cheaped out when element was replaced last time and fitted a small element.

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#2532667 1-Aug-2020 14:05

You know, when it comes to safety it's probably best to get an electrician in to check the wiring and what it can support. Also, you could consider replacing your old fuse with a circuit breaker, available from Mitre 10. I'd link to one but the M10 website doesn't support incoming links, weirdly, just search for "Circuit Breaker" they cost about $30 and often just slot in.

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Technofreak

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#2532716 1-Aug-2020 14:33

I think I've found the answer to the fuse size labelling.

One of the light circuits has a 15 amp fuse and all the rest have 5 amp fuses. I think it's pretty likely the water heater fuse has been mistakenly swapped for one of the light fuses. 15 amps is rather big for a light circuit and 5 amps is rather small for a water heater circuit.

The ambient light where the fuse board is isn't great and it would be easy to not read the label properly and get the fuses mixed up.

I'm beginning to think the 3 kw element will be OK.

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timmmay

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#2532720 1-Aug-2020 14:39

If you're wrong, say hi to the fire service for me ;)

Technofreak

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#2532722 1-Aug-2020 14:46

timmmay:

If you're wrong, say hi to the fire service for me ;)

Do you have expertise on electrical wiring or just offering a laymans input?

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timmmay

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#2532725 1-Aug-2020 14:54

Mostly trolling, but if you're not competent to do this work confidently please at least call an electrician or have them come do this for you. $150 for Weekend call-out could save a lot of hassle or something more serious.

Bung

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#2532730 1-Aug-2020 15:08

Spreading FUD is traditional.

I have 2 x 135l tanks installed around 98. Both were originally supplied with 2000w elements. I believe 3000w elements require 15A switches. If your switch is a round "light switch" style they are only 10A.

Technofreak

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#2532732 1-Aug-2020 15:12

timmmay: Mostly trolling, but if you're not competent to do this work confidently please at least call an electrician or have them come do this for you. $150 for Weekend call-out could save a lot of hassle or something more serious.

I thought so. I did ask for responses from those with expertise to try and avoid getting unhelpful replies.

This is something I am competent to do. It's not an area I work in much these days and as there were a couple of red flags I was looking for confirmation that I was correct.

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#2532733 1-Aug-2020 15:15

Bung: Spreading FUD is traditional.

I have 2 x 135l tanks installed around 98. Both were originally supplied with 2000w elements. I believe 3000w elements require 15A switches. If your switch is a round "light switch" style they are only 10A.

Thank you. The isolation switch is the round light switch.

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gregmcc

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#2532774 1-Aug-2020 15:25

Technofreak:

I think I've found the answer to the fuse size labelling.

One of the light circuits has a 15 amp fuse and all the rest have 5 amp fuses. I think it's pretty likely the water heater fuse has been mistakenly swapped for one of the light fuses. 15 amps is rather big for a light circuit and 5 amps is rather small for a water heater circuit.

The ambient light where the fuse board is isn't great and it would be easy to not read the label properly and get the fuses mixed up.

I'm beginning to think the 3 kw element will be OK.

There are several factors you need to take in to account.

Although the wiring may be 1.5mm (or the nearest imperial size for 70's era), for the distance from the fuse board and the 1.5kw element, 1.5mm may have been the right size, but putting in a 3kw element will turn your wiring in to a heater, this means melting insulation, short circuits and fires.

The next issue will be isolator switch at the hot water cylinder, most likely one of those old round black or white PDL switches with a bit of garden hose style flexible pipe coming out of it with the wires in. These switches were when brand new in the 70's only good for 10amps, now with a 3kw element that 13Amps, another fire in the making.

We won't even venture in to the switchboard with the ceramic fuses.

Save yourself some worry, get and electrician and get it sorted correctly.

larknz

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#2532777 1-Aug-2020 15:29

Back in those days a 1500w element was standard. The wiring is probably 1.5 mm. I haven't looked AS/NZS 3000 for a while but I expect for a 3kW element you will need 2.5mm, which has 7 strands.
Something I meant to mention is that if the switch has a red toggle its rated at 15A, otherwise it's 10A. They used to burn out quite regularly. You need to get everything checked out if you are going to put a bigger element in.
Also what is the thermostat rated for?

sqishy

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#2532779 1-Aug-2020 15:35

I'd say you are ok with 15A fuse and 1.5mm is nominally up to 18A. So 3Kw/230v = 13A. All good.

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#2532781 1-Aug-2020 15:42

sqishy:

I'd say you are ok with 15A fuse and 1.5mm is nominally up to 18A. So 3Kw/230v = 13A. All good.

^^^^^^^^

Don't take this advice as it does not take in to account rating factors and distance from fuse board, and has no consideration for the type of isolation switch that is typically fitted to 70's era houses that will burn out if a 3kw element is installed.

Technofreak

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#2532816 1-Aug-2020 17:17

The hot water cylinder is right beside the switchboard. The wiring is approximately 2 mm sqrd (will be the imperial equivalent I expect) which is heavier than I understand is required (1.5 mm sqrd) for up to 3kw. However in light of the type of isolation switch we have I have swapped the element to the smaller size.

Thanks for all of the helpful replies.

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