Correct Wire Size For 4.5 Kw Shower Heater?

[thaibeachlovers]

Is "normal" power wire size ( 2.5 ) OK, or do I need 4mm? The length from circuit board to shower is 11 meters.

Thanks.

[cheeryble]

If I'm not mistaken 2.5 is standard ring main size in the UK which will handle up to 3kw, presumably that on a spur ie not getting half the current from each direction in the ring.

So to stay proper you need the next size up, which in the UK was 6sqmm though looks like 4 would be perfect if u can be it.

May be cheaper to simply double up the 2.5.

[thaibeachlovers]

If I'm not mistaken 2.5 is standard ring main size in the UK which will handle up to 3kw, presumably that on a spur ie not getting half the current from each direction in the ring.

So to stay proper you need the next size up, which in the UK was 6sqmm though looks like 4 would be perfect if u can be it.

May be cheaper to simply double up the 2.5.

Thanks.

[Crossy]

2.5mm² VAF is good for 22A in air.

Your 4.5kW heater will pull about 20.5A and since it's an intermittent load will be just fine on 2.5mm² protected by a 20A breaker. There is however no spare capacity should you want to upgrade heater in future.

If the cable run is difficult I would pull 4mm² to save issues later in life when the 4.5kW is too small.

BTW, a UK ring is good for a total load of 7.5kW (intermittent up to 10kW), it's each outlet that's limited to 3kW (13A).

[thaibeachlovers]

2.5mm² VAF is good for 22A in air.

Your 4.5kW heater will pull about 20.5A and since it's an intermittent load will be just fine on 2.5mm² protected by a 20A breaker. There is however no spare capacity should you want to upgrade heater in future.

If the cable run is difficult I would pull 4mm² to save issues later in life when the 4.5kW is too small.

BTW, a UK ring is good for a total load of 7.5kW (intermittent up to 10kW), it's each outlet that's limited to 3kW (13A).

Thanks Crossy.

Good to know, as it will save me having to get someone to go up into the roof, which frankly would be dangerous to the person and the ceiling. I'm WAYYYYYY too heavy for the flimsy bits of tin that hold it up.

I have no intention of upgrading further, but the 3.5 is just a little bit too weak in the present cold season and I'm hoping an extra kw will be enough. Certainly will be in the summer.

There is a spare 30 amp breaker in the box. Should I use that, as the heater manual says, or stick with the current 20 amp breaker as not going to 4mm wire?

[cheeryble]

Thanx for the amendment Crossy I was trying to be conservative as it's public advice.......which is why I didn't say "put in one run of 2.5, run at full load, and feel the wire to see if it warms up or not"!

As for the fuse question I say no fuses higher rated than the cable and appliance, ie no 30amp breaker, destroys the point!

Am I right Crossy?

Ps TBL do you mean breaker or switch?

[Crossy]

Try it on the 20A breaker, you should have no issues whatever.

On a single appliance circuit you don't necessarily need to provide overload protection, just short circuit, and 11m of 2.5 should open a 30A breaker pronto in the event of a short so the 30A would also be OK.

EDIT You do have RCD protection on the shower circuit, don't you?

[thaibeachlovers]

Try it on the 20A breaker, you should have no issues whatever. However, if that breaker does open then the 30A should be fine provided there's nothing else on that circuit.

On a single appliance circuit you don't necessarily need to provide overload protection, just short circuit, and 11m of 2.5 should open a 30A breaker pronto in the event of a short.

Thanks for that.

It is indeed the only appliance on that breaker, as I had the original heater installed.

Scarily, everything else in the house goes through two 10 amp breakers, half of the house through one and the other half through the other, though it seems to work. Back when they built the house, the only appliance was the tv, so I guess it was OK then.

[doglover]

When I found out the electrician ran 2.5mm for the 6000W heater I went out an bought some 4mm.... which I aged in the shed for year. Before mustering up the gusto to climb up into the attic I tried a little experiment.

I ran the heater on max with the existing 2.5mm for 5 minutes and checked the water temp. I then ran the approx length (+4M) temporarily across the floor from panel to heater (don't worry, I read flagged the area with danger tape). Ran the heater on max for 5 minutes through the 4mm and checked the water temp. The same! Now I'm no engineer, but I was thinking there would be a difference. Even after the shower runs for 15 minutes on max on the 2.5mm the wires themselves do not feel any warmer than room temp.

So I aged the 4mm another year and then used it for the guesthouse shower. I am not endorsing breaking codes that are in place for very good reasons. But it was just too hard to climb up in the attic for a low level alert with a beer in my hand.

[Artisi]

Love the term - "aged it for a year" .

I have a number of items being aged right now and the question is, do they improve with age like good wine?

[thaibeachlovers]

Thanx for the amendment Crossy I was trying to be conservative as it's public advice.......which is why I didn't say "put in one run of 2.5, run at full load, and feel the wire to see if it warms up or not"!

As for the fuse question I say no fuses higher rated than the cable and appliance, ie no 30amp breaker, destroys the point!

Am I right Crossy?

Ps TBL do you mean breaker or switch?

Sorry, I missed your post before.

Just to catch up, the new 4.5 heater is now installed on the original 2.5 wire and 20 amp circuit breaker and works perfectly. I checked the wire and it doesn't warm up in use. Water is plenty hot enough, so I don't know why anyone would even want a larger kw heater.

It does get hotter than the 3.5 though, so was worth changing it for those cold northern mornings.

Thanks to all that contributed, and I too like the idea of aging things before using, LOL.

[electau]

2,5sqmm will carry 25 amps. Use a 20A MCB. an MCB will carry 1.2 x rated current continuously.

[thaibeachlovers]

2,5sqmm will carry 25 amps. Use a 20A MCB. an MCB will carry 1.2 x rated current continuously.

Thanks for your contribution. Always appreciated.

[212traders]

Just move into an old house. Has a 4.5kW water heater. Whenever we turn on the water heater, our bedroom's lights will go dim. Went up into the attic and discovered that the water heater is using the same wire from the panel as the bedroom's lights & outlets. The wire is 2x2.5mm. The fuse at the panel is CEO MCB-63 C16. Does that mean it's a 16A fuse? Is it too small for the water heater?

[Sceptict11]

Just move into an old house. Has a 4.5kW water heater. Whenever we turn on the water heater, our bedroom's lights will go dim. Went up into the attic and discovered that the water heater is using the same wire from the panel as the bedroom's lights & outlets. The wire is 2x2.5mm. The fuse at the panel is CEO MCB-63 C16. Does that mean it's a 16A fuse? Is it too small for the water heater?

STOP using that shower until the electrics are sorted !

[Crossy]

OK, don't panic, yet.

Is the 2.5 going all the way back to the panel supplying the lights on the way? If it is then no worries. Leaving it as it it with the lights dimming a bit won't cause any serious issues, but do check the joints (which will probably be twist-n-tape). Re-do with wire-nuts if there are any signs of the joint getting warm. You could do the job properly by running a new length of 2.5 back to a 20A breaker at the panel.

If the 2.5 is spliced onto a run of 1.5 that supplies the lights, stop using the shower! Then run a new length of 2.5 back to a 20A breaker at the panel.

The 16A breaker is really too small for the shower but if it's not actually opening in use then that's no worry either, I wouldn't put a bigger breaker in unless you run new wires for the shower direct from the panel.

Whist you're in a DIY mood, check the heater is grounded, when you find it's not run a ground wire, either to a rod near the heater or (better) a rod connected to the ground bus in your board.

Do you have an RCD (Safe-T-Cut) if not consider installing one.

[212traders]

OK, don't panic, yet.

Is the 2.5 going all the way back to the panel supplying the lights on the way? If it is then no worries. Leaving it as it it with the lights dimming a bit won't cause any serious issues, but do check the joints (which will probably be twist-n-tape). Re-do with wire-nuts if there are any signs of the joint getting warm. You could do the job properly by running a new length of 2.5 back to a 20A breaker at the panel.

If the 2.5 is spliced onto a run of 1.5 that supplies the lights, stop using the shower! Then run a new length of 2.5 back to a 20A breaker at the panel.

The 16A breaker is really too small for the shower but if it's not actually opening in use then that's no worry either, I wouldn't put a bigger breaker in unless you run new wires for the shower direct from the panel.

Whist you're in a DIY mood, check the heater is grounded, when you find it's not run a ground wire, either to a rod near the heater or (better) a rod connected to the ground bus in your board.

Do you have an RCD (Safe-T-Cut) if not consider installing one.

Well, since I'm in the DIY mood, please take a look at the panel and a sample photo of the wiring I had to deal with.

It seems that the panel is full and I might not have room for additional separate fuse for the water heater. If no more room for additional fuse, should I just replace the existing 2.5mm with 4mm and continue to share the water heater wiring with the lighting and the outlets in the room?

[thomasteve]

What a mess !! - needs some major surgery.

[bankruatsteve]

It would probably help if you could identify what each circuit (6?) is for. Agree, it looks messy but maybe there is some logic to it. (or not) And, it appears different size wires are being connected. Can you identify for that? Is that your shower circuit?

Yeah, if everything is easy to re-do - you might want to do that - but have a circuit plan first.

[Crossy]

Apart from the spaghetti I see:

1. A board with no ground bar
2. No earth leakage protection (RCD)
3. A worryingly unconnected green wire
4. Three 32A breakers, what do they supply?
5. A couple of fat wires not connected, where do they go?

I would, in order of priority in line with Forky's pinned thread:

1. Install an RCD in that double space next to the main switch
2. Get a rod in and ground the shower heater
3. Tidy up the spaghetti and ensure each circuit has an appropriate wire size and breaker
4. If not a rental replace the board with a unit with a ground bar and get some grounded outlets installed for Class-1 appliances.

It's not clear in the photo, what rating is the incoming breaker? What meter do you have, it will be marked 5/15, 15/45 or 30/100?

If you have a 5/15 supply that may explain the dimming lights.

[212traders]

I plan to re-wire the whole house. But before I do, I need to plan out the new electrical wiring design. I have come out with the following 2 designs using the existing panel (see hi-res photo):

Design 1

Breaker 1 (20A) using 2.5mm wire: all lighting and outlets for the living room (service area).

Breaker 2 (32A) using 4mm wire: all lighting and outlets for 1^st bedroom and its bathroom (including 4500W water heater).

Breaker 3 (32A) using 4mm wire: all lighting and outlets for 2^nd bedroom and its bathroom (including 4500W water heater).

Breaker 4 (32A) using 4mm wire: all lighting and outlets for kitchen

Breaker 5 (20A) using 4mm wire: outside lighting and outlets (including outside bedroom)

Breaker 6 (20A): spare

Design 2

Breaker 1 (32A) using 4mm wire: all lighting and outlets for the living room (service area) AND outside lighting/outlets (including outside bedroom).

Breaker 2 (20A) using 2.5mm wire: all lighting and outlets for 1^st bedroom

Breaker 3 (20A) using 2.5mm wire: 1^st bathroom (including 4500W water heater).

Breaker 4 (20A) using 2.5mm wire: all lighting and outlets for 2^nd bedroom

Breaker 5 (20A) using 2.5mm wire: 2^nd bathroom (including 4500W water heater).

Breaker 6 (32A) using 4mm wire: all lighting and outlets for kitchen

What do you think?

[Crossy]

Do not put your water heaters on the same circuit as the outlets and lighting. A 32A breaker won't protect the outlets from overload when Uncle plugs his 6kW welder into one (the 4mm² would be fine, the 16A rated outlets won't).

If you're doing a rewire I would replace that consumer unit with one with an earth bar (or if on a budget add an earth bar to the one you have), add a ground rod, install 3 pin outlets and ground things properly, a front end RCD or RCBO is non-negotiable.

I would do it like this:-

1 - Water heater 1, 4mm² cable, 32A breaker

2 - Water heater 2, 4mm² cable, 32A breaker

3 - Upstairs lighting and outlets, 2.5mm² cable 16/20A breaker

4 - Downstairs lighting and outlets (including kitchen if indoors), 2.5mm² cable 16/20A breaker

(I'm assuming a 2 floor home here, if not split it sensibly between these two circuits)

5 - Outside lighting and outlets (including kitchen if outdoors), 2.5mm² cable 16/20A breaker

6 - Spare

Use 10mm² for any internal wiring in the distribution board.

Note, there's nothing to stop you having lighting and outlets on the same circuit, many local homes are wired this way. You can use 1.5mm² for the switch runs and lighting droppers to save a little cash, but be aware that someone may come along and add an outlet somewhere and hook to the convenient 1.5mm² cable.

EDIT. Looking at your more recent photo I see that your distribution board DOES have both Neutral and Ground bars (one is hidden behind the spaghetti), one should be on insulators (Neutral) the other bolted to the metalwork (Ground).

[Forkinhades]

Just to add for the water heater you can use 2.5mm2 up to 25 meters with an 4% V.D. Allocated. On a 20 Amp MCB

4mm no more than 44 meters, on a 20 A or 32 A

4mm is good for future upgrades.

[Forkinhades]

^ Note to above calculation was done using 230V (19.56A)

220V gives 20.45 A

[Forkinhades]

A 2.5mm cable can carry 27A

[212traders]

Do not put your water heaters on the same circuit as the outlets and lighting. A 32A breaker won't protect the outlets from overload when Uncle plugs his 6kW welder into one (the 4mm² would be fine, the 16A rated outlets won't).

If you're doing a rewire I would replace that consumer unit with one with an earth bar (or if on a budget add an earth bar to the one you have), add a ground rod, install 3 pin outlets and ground things properly, a front end RCD or RCBO is non-negotiable.

I would do it like this:-

1 - Water heater 1, 4mm² cable, 32A breaker

2 - Water heater 2, 4mm² cable, 32A breaker

3 - Upstairs lighting and outlets, 2.5mm² cable 16/20A breaker

4 - Downstairs lighting and outlets (including kitchen if indoors), 2.5mm² cable 16/20A breaker

(I'm assuming a 2 floor home here, if not split it sensibly between these two circuits)

5 - Outside lighting and outlets (including kitchen if outdoors), 2.5mm² cable 16/20A breaker

6 - Spare

Use 10mm² for any internal wiring in the distribution board.

Note, there's nothing to stop you having lighting and outlets on the same circuit, many local homes are wired this way. You can use 1.5mm² for the switch runs and lighting droppers to save a little cash, but be aware that someone may come along and add an outlet somewhere and hook to the convenient 1.5mm² cable.

EDIT. Looking at your more recent photo I see that your distribution board DOES have both Neutral and Ground bars (one is hidden behind the spaghetti), one should be on insulators (Neutral) the other bolted to the metalwork (Ground).

First of all, I want to thank you for all your guidance. I really appreciated.

One thing I failed to mention is that there are 2 A/C units, one in bedroom 1 and the other in the living room. Will this change your suggestion?

[Crossy]

Do not put your water heaters on the same circuit as the outlets and lighting. A 32A breaker won't protect the outlets from overload when Uncle plugs his 6kW welder into one (the 4mm² would be fine, the 16A rated outlets won't).

If you're doing a rewire I would replace that consumer unit with one with an earth bar (or if on a budget add an earth bar to the one you have), add a ground rod, install 3 pin outlets and ground things properly, a front end RCD or RCBO is non-negotiable.

I would do it like this:-

1 - Water heater 1, 4mm² cable, 32A breaker

2 - Water heater 2, 4mm² cable, 32A breaker

3 - Upstairs lighting and outlets, 2.5mm² cable 16/20A breaker

4 - Downstairs lighting and outlets (including kitchen if indoors), 2.5mm² cable 16/20A breaker

(I'm assuming a 2 floor home here, if not split it sensibly between these two circuits)

5 - Outside lighting and outlets (including kitchen if outdoors), 2.5mm² cable 16/20A breaker

6 - Spare

Use 10mm² for any internal wiring in the distribution board.

Note, there's nothing to stop you having lighting and outlets on the same circuit, many local homes are wired this way. You can use 1.5mm² for the switch runs and lighting droppers to save a little cash, but be aware that someone may come along and add an outlet somewhere and hook to the convenient 1.5mm² cable.

EDIT. Looking at your more recent photo I see that your distribution board DOES have both Neutral and Ground bars (one is hidden behind the spaghetti), one should be on insulators (Neutral) the other bolted to the metalwork (Ground).

First of all, I want to thank you for all your guidance. I really appreciated.

One thing I failed to mention is that there are 2 A/C units, one in bedroom 1 and the other in the living room. Will this change your suggestion?

If you want to re-use the same consumer unit, and the A/Cs are not over about 18,000 BTU you can put them on the outlet supply for the room, normally you'd give them their own breaker like the water heater.

[212traders]

The A/C in the living room is 25,000BTU. The one in the bedroom is 18,000BTU.

[Crossy]

The A/C in the living room is 25,000BTU. The one in the bedroom is 18,000BTU.

They will need their own breakers and wiring then, 2.5mm² cable and a 20A breaker for each.

You are going to have to replace that distribution board with a larger unit to get all the breakers and an RCD in.

Those are pretty meaty A/C units, how big are the rooms?

[212traders]

Thanks for all the info. Now I just need to plan my schedule of work and buying of materials.