Water heater

[Ed Evans]

A customer of mine has asked for a water heater to be installed that will satisfy a kitchen and bathroom. No room heating. Any suggestions.

 

[telectrix]

have installed a few 9kW under sink heaters, switch on when hot tap is operated. but would suggest separate units, one for each room. each on it's own dedicated 40A or 50A circuit, with local 45A isolation. 6mmcable may just do depending on length of run and installation method, but you may need to specify 10mm.
bear in mind that overload protection is not required, only fault protection.

 

[bill01803]

How close together are the rooms?

 

[telectrix]

How close together are the rooms?

hope they're more than 2m. can't have bathroom corona transferred to a kitchen.

 

[buzzlightyear]

How close together are the rooms?

possibly they put a glass to the walls.

 

[davesparks]

A customer of mine has asked for a water heater to be installed that will satisfy a kitchen and bathroom. No room heating. Any suggestions.

How much space is available?
Do you want instantaneous or stored?

 

[John-SJW]

Many options. If instant water heating is needed, then one 11.5 kW instant water heater can be fitted. 11.5 kW is the maximum on a single phase supply.

Look into instant hot water taps. A Qooker type of tap for the kitchen also giving boiling water, so the kettle can be ditched to liberate worktop space. The 11.5 kW instant water heater can then just do the bathroom with the kitchen hot tap draw-off not influencing the shower. Of course bath fills will not be brilliant. If a shower only, a great way to go, but have an eco aerated shower head.

 

[John-SJW]

Assuming a 100A supply of course.
[automerge]1591029222[/automerge]

bear in mind that overload protection is not required, only fault protection.

I find that crazy. No overload protection. How many would leave it out?

 

[telectrix]

Assuming a 100A supply of course.
[automerge]1591029222[/automerge]
I find that crazy. No overload protection. How many would leave it out?

how can it overload. it's a fixed load. it can go open, in which case it won't work, or it can short (or the cable to it) in which case you have short circuit protection (fault protection).

 

[John-SJW]

You can still get overload (a fault) without fault protection kicking in.

 

[davesparks]

You can still get overload (a fault) without fault protection kicking in.

How can you get an overload on a fixed resistive load such as a water heater?

 

[John-SJW]

How can you get an overload on a fixed resistive load such as a water heater?

The element cover can break down with the L in contact with water raising the current draw not tripping on fault but overload. I have seen it happen. If there is a spur off a 32A ring via a J-box, only to say an immersion heater element, I believe the regs say no fuse is needed on that spur (fixed restive load), while everything else seems to need one, even a spur to a garden office or garage - not 100% sure on that. To me that is total nonsense. The cost of putting in over-current protection is pennies.

 

[pc1966]

The cost of putting in over-current protection is pennies.

There is (almost) always will be over current protection as the regulations require protection of cable against a short.

But overload protection is not always required as some loads should not have the possibility of an overload fault. As you point out, that might be an optimistic assumption in real life!

It is a bit like the requirements for RCD protection, these days the majority of domestic circuits require it (for one reason or another) but not for things like fixed heaters. Which is a shame as that is exactly the sort of thing best suited to picking up a partial heater element fault!

 

[davesparks]

The element cover can break down with the L in contact with water raising the current draw not tripping on fault but overload. I have seen it happen.

The cost of putting in over-current protection is pennies.

That is not an overload situation, the load has not been increased over its design limits, that is a fault. Albeit a very rare and unusual fault that will take a long time to clear.

The cost of designing with overcurrent protection in place on a domestic job is usually a matter of pennies or pounds yes, but there is a whole world outside of domestic work where it can be a very different story.

 

[pc1966]

For a heater the distinction is probably academic, if you have a load taking X amps then you size your cable for that and fit a MCB at the matching level. So it would be unusual for the OCPD not to also provide overload protection.

Where you see the difference is something like a garage feed (again!) when you might have a planned load of, say, 20A and select a cable to match, then the garage CU has a 20A MCB that provides the overload protection. But the feed for the cable might be a 40A or more fuse that will clear in under 5s on a short but is not offering overload protection for the 20A-rated cable.