Water heater wire size

[Mike45]

I've had a shower water heater in

MIL house in the village for years. Its 3500 watts.

Its time to be replaced.

The water has never been hot and sometimes not even warm depending on water volume. I'm thinking that the wire size might be undersized.

Its about a 50 foot distance from main panel and heater.

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[Forkinhades]

By calculation 1.5mm is ok for a 16 amp load over 15 meters for your live and neutral, but you will need 2.5mm for your earth.

Personally I would go for 2.5mm for all cables. Gives options for upgrade.

How will you run the cable? In conduit? Clipped direct? What type of cable will you use?

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[Crossy]

Yup ^^^

And, importantly, how powerful is the heater you intend installing.

What meter size does the MiL have (5/15, 15/45 or something else)?

[Mike45]

By calculation 1.5mm is ok for a 16 amp load over 15 meters for your live and neutral, but you will need 2.5mm for your earth.

Personally I would go for 2.5mm for all cables. Gives options for upgrade.

How will you run the cable? In conduit? Clipped direct? What type of cable will you use?

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So the lack of hot water is not because the wires are undersized?

Looking at that breaker that has power tapped off the outlet plug I can see what looks like two white and black 1.5mm wires but I don't see a ground wire. The outlet that its connected to doesn't have a ground pin on it.

I looked at the main switches and don't see a ground wire. I don't think there is any grounds in the house so the water heater must not have one either.

The meter is a 5/15.

So why hasn't the water ever really gotten hot except when you turn it down to a drizzle?

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[Mike45]

Yup ^^^

And, importantly, how powerful is the heater you intend installing.

What meter size does the MiL have (5/15, 15/45 or something else)?

I have as going to install another 3500W because I assumed the wires were the problem.

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[thomasteve]

You will need more than about 5 or 6 kW to get a decent flow of hot water as it depends on how cold the incoming water is.

[bankruatsteve]

You will need more than about 5-6 kW to get a decent flow of hot water depends on how cold the incoming water is.

If there's no flow control and gushing cold water, that very well could be the requirement. BUT, most units do have flow control and 3.5 KW will deliver a decent shower for most folks. For those that need jet spray and HOT - better to get a water heater than the on-demand high KW.

[Mike45]

You will need more than about 5-6 kW to get a decent flow of hot water depends on how cold the incoming water is.

If there's no flow control and gushing cold water, that very well could be the requirement. BUT, most units do have flow control and 3.5 KW will deliver a decent shower for most folks. For those that need jet spray and HOT - better to get a water heater than the on-demand high KW.

I don't need a jet spray or very hot. Curiously our showers last night were actually hot. I have no idea why!

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[Mike45]

You will need more than about 5-6 kW to get a decent flow of hot water depends on how cold the incoming water is.

If there's no flow control and gushing cold water, that very well could be the requirement. BUT, most units do have flow control and 3.5 KW will deliver a decent shower for most folks. For those that need jet spray and HOT - better to get a water heater than the on-demand high KW.

There is a flow control. Normally it has be turned way way down to get anything resembling warm water.

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[IMHO]

These heaters have startup current demand around 125% (or more) of rated power.

We always use 4mm2/20A breaker for heaters < 4000W, and 6mm2/32A breaker for heaters > 4000W.

[IMHO]

You will need more than about 5-6 kW to get a decent flow of hot water depends on how cold the incoming water is.

If there's no flow control and gushing cold water, that very well could be the requirement. BUT, most units do have flow control and 3.5 KW will deliver a decent shower for most folks. For those that need jet spray and HOT - better to get a water heater than the on-demand high KW.

I don't need a jet spray or very hot. Curiously our showers last night were actually hot. I have no idea why!

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Could be a supply voltage drop problem... Does your microwave still work with the hot water running?

[Mike45]

You will need more than about 5-6 kW to get a decent flow of hot water depends on how cold the incoming water is.

If there's no flow control and gushing cold water, that very well could be the requirement. BUT, most units do have flow control and 3.5 KW will deliver a decent shower for most folks. For those that need jet spray and HOT - better to get a water heater than the on-demand high KW.

I don't need a jet spray or very hot. Curiously our showers last night were actually hot. I have no idea why!

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Could be a supply voltage drop problem... Does your microwave still work with the hot water running?

Don't have a microwave in the village.

However during my morning shower the main breaker tripped. The small clothes washer,a couple of fans and a 9000 btu Ac were running at the same time.

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[IMHO]

Don't have a microwave in the village.

However during my morning shower the main breaker tripped. The small clothes washer,a couple of fans and a 9000 btu Ac were running at the same time.

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OK, well next step is to try and find someone with a multimeter, so you can test for voltage drop I guess.

[bankruatsteve]

Don't think the OP ever said what size meter. Chances are he's on 5/15 and tripping a 10a breaker.

[Forkinhades]

They did in post #4

5/15

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[Mike45]

Don't think the OP ever said what size meter. Chances are he's on 5/15 and tripping a 10a breaker.

The breaker at the wall switch is 30A and has never tripped. Its the big one for the whole house in post 4 next to the knife switch. I have no idea what it is rated....do you?

Also are we protected from electrocution? We have no ground in the house and the switch is a normal breaker at 30A.

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[IMHO]

Don't think the OP ever said what size meter. Chances are he's on 5/15 and tripping a 10a breaker.

The breaker at the wall switch is 30A and has never tripped. Its the big one for the whole house in post 4 next to the knife switch. I have no idea what it is rated....do you?

Also are we protected from electrocution? We have no ground in the house and the switch is a normal breaker at 30A.

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Breakers do not protect people from electrocution. Your water heater should have a built in RCD, but that won't work if it's not grounded.

[thomasteve]

Don't think the OP ever said what size meter. Chances are he's on 5/15 and tripping a 10a breaker.

The breaker at the wall switch is 30A and has never tripped. Its the big one for the whole house in post 4 next to the knife switch. I have no idea what it is rated....do you?

Also are we protected from electrocution? We have no ground in the house and the switch is a normal breaker at 30A.

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Breakers do not protect people from electrocution. Your water heater should have a built in RCD, but that won't work if it's not grounded.

It should still trip even if there's no earth / ground wire connected but don't risk it - in addition fit a saf-t-cut device or similar RCD at the main box and make sure there is correct earthing and a ground rod installed.

[wayned]

Although there are no visable markings on it,the unit next to the knife switch in post #4 looks a safety cutout switch and it might just be saving your life! If it is tripping when you turn on the shower, it is either defective or is doing its job by detecting an imbalance in the current flow between the live and neutral wires.

You either have a serious wiring problem, a defective water heater whose internal safety switch is not working or a defective switch that is pictured in post #4. You should get a qualifeied electrician - good luck - to troubleshoot and repair the problem before someone gets hurt, or worse. He should also install a ground rod at the same time.

[Crossy]

We had a similar device to the two-button beast in the photos in our apartment in Rome, it was purely an over-current device, no earth leakage protection.

I've just updated the FAQ with Does my RCD need a ground to operate?

Answer repeated here:-

An RCD senses the difference between the current in the Live conductor and the current in the Neutral conductor, any difference greater than the trip current is assumed to be going where it shouldn't (through you) and the device operates.

This means that the RCD does not actually NEED an earth or an earthed system to function and provide protection from potentially fatal shock.

BUT

Say a device that should be grounded (your water heater) is operated without a ground and then develops a L-E fault causing the metalwork to become live.

With no ground connection the heater sits there innocently awaiting the first mug to come along and touch the metalwork at which point a current flows to earth through the victim and, hopefully, the RCD operates and saves his life.

If the same device has been correctly grounded, when it develops the L-E fault the current immediately flows to earth and operates the trip, no need for a victim to act as part of the circuit.

Why does this matter, the RCD operated both times? The 30mA trip current chosen internationally for domestic RCDs is a trade-off between being too sensitive (and tripping all the time) and being fatal. 30mA for 30ms is generally accepted as being non-lethal to 90% of the healthy adult population, the elderly, very young or sick may have a lower tolerance and could actually be killed even though the RCD operates.

Get that heater earthed.

[IMHO]

We had a similar device to the two-button beast in the photos in our apartment in Rome, it was purely an over-current device, no earth leakage protection.

I've just updated the FAQ with Does my RCD need a ground to operate?

Answer repeated here:-

An RCD senses the difference between the current in the Live conductor and the current in the Neutral conductor, any difference greater than the trip current is assumed to be going where it shouldn't (through you) and the device operates.

This means that the RCD does not actually NEED an earth or an earthed system to function and provide protection from potentially fatal shock.

BUT

Say a device that should be grounded (your water heater) is operated without a ground and then develops a L-E fault causing the metalwork to become live.

With no ground connection the heater sits there innocently awaiting the first mug to come along and touch the metalwork at which point a current flows to earth through the victim and, hopefully, the RCD operates and saves his life.

If the same device has been correctly grounded, when it develops the L-E fault the current immediately flows to earth and operates the trip, no need for a victim to act as part of the circuit.

Why does this matter, the RCD operated both times? The 30mA trip current chosen internationally for domestic RCDs is a trade-off between being too sensitive (and tripping all the time) and being fatal. 30mA for 30ms is generally accepted as being non-lethal to 90% of the healthy adult population, the elderly, very young or sick may have a lower tolerance and could actually be killed even though the RCD operates.

Get that heater earthed.

I'll add to this, when Crossy says 30mA is non-fatal, that doesn't mean it's non-painful! I have permanent muscle damage to one of my shoulders from a 30mA shock a few years ago.

[Mike45]

I look around me here in my MIL village house that my family needs to stay in for a couple of months and all I see is old, very young and pregnant people. I'm convinced that the entire electrical system needs a ground and especially the water heater and AC. At my request my FIL has called the local electrical guy to come and give us a quote.

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[Mike45]

For 5/15 meter what size main circuit breaker should it be?

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[Crossy]

For 5/15 meter what size main circuit breaker should it be?

I'd be looking at 20A

[Mike45]

I admit I know next to nothing but I expected you to suggest a larger value. My thought process is if a 15/45 gets a 63A I figured a 5/15 would be maybe 30A

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[Crossy]

I admit I know next to nothing but I expected you to suggest a larger value. My thought process is if a 15/45 gets a 63A I figured a 5/15 would be maybe 30A

I do tend to err on the safe side, 30A would likely be just fine. The meters are incredibly robust but we have had reports on the forum of 5/15's failing catastrophically.

If it's a new installation your local PEA office will give you their requirements. I installed a 63A incomer on our 15/45 and the inspector insisted I change it to a 50A, he even came back to check (and have another beer). That said, it's never opened even when I peaked our load at 60A, if it ever does the 63A is waiting in the wings.

[Mike45]

I admit I know next to nothing but I expected you to suggest a larger value. My thought process is if a 15/45 gets a 63A I figured a 5/15 would be maybe 30A

I do tend to err on the safe side, 30A would likely be just fine. The meters are incredibly robust but we have had reports on the forum of 5/15's failing catastrophically.

If it's a new installation your local PEA office will give you their requirements. I installed a 63A incomer on our 15/45 and the inspector insisted I change it to a 50A, he even came back to check (and have another beer). That said, it's never opened even when I peaked our load at 60A, if it ever does the 63A is waiting in the wings.

I went looking in the big box stores and I found that all the populated CU that have RCBO have either 63A, 50A or 32 A.

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[Mike45]

I admit I know next to nothing but I expected you to suggest a larger value. My thought process is if a 15/45 gets a 63A I figured a 5/15 would be maybe 30A

I do tend to err on the safe side, 30A would likely be just fine. The meters are incredibly robust but we have had reports on the forum of 5/15's failing catastrophically.

If it's a new installation your local PEA office will give you their requirements. I installed a 63A incomer on our 15/45 and the inspector insisted I change it to a 50A, he even came back to check (and have another beer). That said, it's never opened even when I peaked our load at 60A, if it ever does the 63A is waiting in the wings.

Oh and its not a new installation. Just trying the make the MIL house place, that my family is staying in while waiting for the new house to finish safe and comfortable.

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[Mike45]

I found a CU with a 32A MCB with an adjustable RCBO next to it. I didn't buy it because I was confused when I looked inside. I didn't see separate ground and return bars.

I don't know if the village is MEN or not. I showed a photo of the main panel in an earlier post.

I'd like some advice how to proceed.

Meanwhile I have installed a1.2 meter ground rod and I have run 2.5mm green wire to all the outlets. I've replaced all 2 prong outlets with three prong and have attached the grounds. I've grounded the water heater, refrigerator and A/C.

Can you advise about the CU and how I should address whether its MEN or not? Thanks

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[Mike45]

I've found two CU. One by CKY and one by critter

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