Hand driers

[MalcyB]

Hi all

I am used to just doing domestic, but I've been asked to supply & install 4 hand driers in our local village hall. One of them I might be able to spur into an existing socket (I have to check first).

The other three I thought I would put on their own circuit, 4mm radial, on a 20A rcbo. The length of run would be about 28mts. Enclosed in either trunking or conduit.

The driers I've seen are about 2.5kw each.

Would diversity come into play on this? And do you think I'm going overboard with a 4mm cable?

Anyone recommend any driers?

Thanks

Malc

 

[septiclecky]

Hi allI am used to just doing domestic, but I've been asked to supply & install 4 hand driers in our local village hall. One of them I might be able to spur into an existing socket (I have to check first).

The other three I thought I would put on their own circuit, 4mm radial, on a 20A rcbo. The length of run would be about 28mts. Enclosed in either trunking or conduit.

The driers I've seen are about 2.5kw each.

Would diversity come into play on this? And do you think I'm going overboard with a 4mm cable?

Anyone recommend any driers?

Thanks

Malc

Do you mean each one on it's own circuit protected by a 20A RCBO or all 3 on a 20A RCBO?

If you put 3 on together the is a chance that the RCBO tripping if all 3 come on together.

No diversity in my opinion.

 

[MalcyB]

All three on the same trip. I thought the chance of all three coming on together was unlikely? One is in the gents, one in the ladies the other in a disabled toilet.

 

[a1]

All three on the same trip. I thought the chance of all three coming on together was unlikely? One is in the gents, one in the ladies the other in a disabled toilet.

Maybe they have more chance of coming on together, that way?

 

[ProDave]

All three on the same trip. I thought the chance of all three coming on together was unlikely? One is in the gents, one in the ladies the other in a disabled toilet.

VERY likely all 3 will come on together.

But the solution is obvious. Each 2.5KW dryer will take about 10.5A, so put the 3 dryers on your 4mm radial but with a 32A MCB (or RCBO ) and they will all run hapilly together all day long.

 

[Apache]

All three on the same trip. I thought the chance of all three coming on together was unlikely? One is in the gents, one in the ladies the other in a disabled toilet.

Nah - think if there's been a play on. At the end or in the middle everyone goes to the toilet! Like the world cup and boiling kettles.

I'm sure you will but see how many great coffee urns they run off the same ring circuit as you are intending to spur off as they do draw a fair few amps....

 

[Lee321]

as dave says. or more put 1 on this local circuit you have eye'd up and the other 2 on new circuit

type c too

 

[Andy™]

VERY likely all 3 will come on together.But the solution is obvious. Each 2.5KW dryer will take about 10.5A, so put the 3 dryers on your 4mm radial but with a 32A MCB (or RCBO ) and they will all run hapilly together all day long.

^ what he says.

but it may need 6mm depending on VD

 

[stani]

unfortunately each handdryer will take 10.87 amps which equals 32.6 all together, 4.00mm over your 28metres will take 37amps max, so you cant even up rate to 40amp mcb, best split 3 seperate and run 2.5mm, if you use

http://www.tlc-direct.co.uk/Technical/Charts/VoltageDrop.html

they have an excellent easy to use volt drop calculator, takes all the hassle out of weary eyes and brains at the end of the day.

 

[Andy™]

unfortunately each handdryer will take 10.87 amps which equals 32.6 all together, 4.00mm over your 28metres will take 37amps max, so you cant even up rate to 40amp mcb, best split 3 seperate and run 2.5mm, if you usehttp://www.tlc-direct.co.uk/Technical/Charts/VoltageDrop.html

they have an excellent easy to use volt drop calculator, takes all the hassle out of weary eyes and brains at the end of the day.

chances are, each dryer will be rated at 240V. working at 230v, it will use less. and i dont think anyone is bothered about 0.6A anyway.

 

[ProDave]

unfortunately each handdryer will take 10.87 amps which equals 32.6 all together

I personally would be comfortable with 32.6A on a 32A MCB. I'm willing to bet that a) it would run all day at that without tripping, and B) as already suggested the actual current will be less, especially if you take into account the reduction due to volt drop. However in a possibly borderline case like this, I would measure the actual current drawn with all 3 running after installing just to make sure.

Also hand dryers usually only run for 30 seconds or so at a time unless re triggered, so it's not a continuous load.

My suggestion of using a 32A MCB was to avoid tripping if all 3 happen to get used at once, which almost certainly would very quickly trip the 20A MCB proposed originally.

 

[Sidewinder]

BS 60898 B20 will trip at 30A in around 1500 seconds, and at 40A in around 175 seconds.

Difficult to exactly interpolate times on a log/log graph.

BTW Pg 249.

 

[MalcyB]

Thanks for all the replies.

I did wonder about using 2.5 t/e on a ring but thought it would be easier on a radial.

Because of the uncertanty I have decided to change the dryers to 2.2Kw.

Thanks Stani, the TLC vd calculator is very handy.

According to that, I'd have a load of 28.7A. It will be in conduit, but not in any insulation, so 4mm should be ok protected by a 32A rcbo.

 

[stani]

No problem mate, the TLC is quite good as a guide, it means you dont have to get the 17th edition out every time and try and do loads of maths. good luck with the dryers.

 

[Doc Hudson]

I have noticed the use of lower wattage driers at some service stations and public buildings over recent months. Green thinking maybe?

Doc H.

 

[Sidewinder]

Doc,

Maybe not, it just takes longer to dry your hands?...

Thus the same overall energy consumption?

Take a kettle, it takes a certain amount of energy to heat a certain volume of water from x deg to y deg.

At a lower voltage the power is less thus it just takes longer, thus there is more heat loss through the boundaries of the vessel, so does it save energy in this case?

Slightly different to the hand dryer I know...

 

[batty]

Doc,Maybe not, it just takes longer to dry your hands?...

Thus the same overall energy consumption?

Take a kettle, it takes a certain amount of energy to heat a certain volume of water from x deg to y deg.

At a lower voltage the power is less thus it just takes longer, thus there is more heat loss through the boundaries of the vessel, so does it save energy in this case?

Slightly different to the hand dryer I know...

Or could be they think people will get fed up hanging around waiting for them to dry and will go off with damp hands.

 

[Sidewinder]

True, but, I once spent a week at Uni with a viral microbiologist!

He was adamant that after going to the small room and washing you hands, not drying them fully was worse than not washing them as the damp environment is a better breeding ground!

:coat