Storage Heater Sizing

[harold_dcfc]

Hi

I will soon be fitting a 0.9kw storage heater. it has no user controls so I will be using a d/p fused timer switch (recommended in installation instructions) I will be using 1.5mm heat resistant flex from the dp switch to the heater, but am just wondering if I should use 2.5mm to power the dp switch as it has a 13A fuse. or can I down size this as the storage heater will use around 4Amps.

As im newly qualified and don't have any experience with storage heaters I thought would just check to be sure. I would either use 1.5mm to the dp switch with a 6A RCD if could downsize the fuse. Or if not 2.5mm to the 13A dp fused spur with a 16A RCD.

Look forward to your advice/comments

 

[ArseyDee]

This is a rehash of an earlier post. Storage heater in a bathroom.....

 

[micknew]

Should be in the Diy section.

 

[ArseyDee]

micknew and I are both unhelpful 'Kents'!!

 

[MDJ]

Hi

I will soon be fitting a 0.9kw storage heater. it has no user controls so I will be using a d/p fused timer switch (recommended in installation instructions) I will be using 1.5mm heat resistant flex from the dp switch to the heater, but am just wondering if I should use 2.5mm to power the dp switch as it has a 13A fuse. or can I down size this as the storage heater will use around 4Amps.

As im newly qualified and don't have any experience with storage heaters I thought would just check to be sure. I would either use 1.5mm to the dp switch with a 6A RCD if could downsize the fuse. Or if not 2.5mm to the 13A dp fused spur with a 16A RCD.

Look forward to your advice/comments

Hi Harold, you say newly qualified, can you go deeper into this M8, You may find the DIY section less aggressive, it is really basic stuff, let us know your qualifications and we can then decide how far to go due to the fact it is a bathroom Job and a special location.

 

[kingeri]

Whether for storage heaters or not, this is basic circuit design.

 

[Zebra Stripe]

Harold, hold fast,, stand ya ground, and let em have it with your design calculations...:freak:

 

[harold_dcfc]

I qualified 6 months ago and only work in industrial locations, brewery's power stations etc. but have done a small amount of domestic in my apprenticeship. I know this is a special location as a bathroom and the dp switch/ storage heater will be installed 0.8m from the bath so just outside zone 2

 

[MDJ]

This is a rehash of an earlier post. Storage heater in a bathroom.....

http://www.electriciansforums.co.uk/central-heating-systems/85588-storage-heater.html

 

[MDJ]

I qualified 6 months ago and only work in industrial locations, brewery's power stations etc. but have done a small amount of domestic in my apprenticeship. I know this is a special location as a bathroom and the dp switch/ storage heater will be installed 0.8m from the bath so just outside zone 2

It is the fact you know the heater will only pull 3.9 amps, you are connecting a 1.5 flex to it and have decided on a 6 amp Protective device yet are asking about cable sizing, how far from the DB is the spur? what is the cable reference? regardless 1.5 will be fine I am sure.

 

[harold_dcfc]

The spur is 18m from the DB and cable ref. B (PVC Trunking) for below the loft. In the loft I will be going through the joists under 100mm thick insulation not sure of ref for this

 

[Zebra Stripe]

Storage heater in a bathroom just seems weird, although any heater in a bathroom seems odd to me....whats wrong with ya all, do you all bath in cold water??:chinese:

 

[MDJ]

In the loft I will be going through the joists under 100mm thick insulation not sure of ref for this

Now we are getting somewhere Harold, although the 1.5mm2 Cable will be fine for this 3.9 amp load even under insulation I would personally try to avoid it and clip to the beams around the loft if possible and To be honest I would stick some 2.5mm2 cable in as standard anyhow regardless because I carry it on the van, Can you avoid the insulation?

 

[harold_dcfc]

As I will be going through the joists I could avoid the insulation if I was to run a form of containment over each joist, although this can change ref.

 

[MDJ]

As I will be going through the joists I could avoid the insulation if I was to run a form of containment over each joist, although this can change ref.

Ref 101 at the Mo, no big deal, but you could clip to the beams and just pop into the loft floor where you need to drop to the bathroom surely, anyhow, smack a 2.5mm2 cable in and forget all about it

 

[harold_dcfc]

Ok thanks for your advice, would I be correct to use a 6A RCD and place a 6A fuse in dp fused switch?

 

[MDJ]

Ok thanks for your advice, would I be correct to use a 6A RCD and place a 6A fuse in dp fused switch?

You cannot get a 6 amp fuse for a spur unit, they come in 2, 3, 5, 10 and 13, stick a 5 in, however that said the breaker will trip first anyhow under fault conditions, the fuse will take some blowing.

 

[harold_dcfc]

Thank you for your education

 

[MDJ]

Thank you for your education

No worries, remember the Breaker is there to protect the cable, so a 2.5mm2 cable on a 6 amp RCBO will be perfectly safe, have fun.

 

[ArseyDee]

As I will be going through the joists I could avoid the insulation if I was to run a form of containment over each joist, although this can change ref.

Careful with the diameter of holes in the joists (especially in older properties). Have seen a few ceilings collapse following over zealous joist drilling. 2nd floor ceiling joists in older properties just don't have the depth of timber to cope with oversized holes and the weight of the roof.