Water heaters in new school

[cliffed]

thoughts on this,on drawings, water heaters are on a ring main circuit,dedicated to the heaters,there are 4 of these.
Listening to spark ninja this could prove a problem with the overloading & balancing of this ring.
Why would consultants decide on a ring ,instead,like the good old days,all heaters are cabled back.

 

[Wilko]

Hi - tell us a bit more about the loads and the RFC design and I'm sure you'll get plenty of commentary .

 

[cliffed]

They are 4 x 3kw heaters on ring circuit,approximately 60 meters of cabling,rcbo 32 amp c type.

 

[Wilko]

They are 4 x 3kw heaters on ring circuit,approximately 60 meters of cabling,rcbo 32 amp c type.

Last I checked 3kW is 12.5A at 240V and so 4 heaters means 50A. I would assume all heaters will be on together first thing in the morning, so no diversity. Maybe I've missed something ...

 

[cliffed]

Agree,pretty pathetic design.

 

[tlangdon12]

If the water heaters don't store any water, they are of the instantaneous type and the On-site Guide suggests an allowance for diversity for such heater that results in the maximum demand being 32.6A. Given the UK power supply is often above 230V, I would say that this load is acceptable on a 32A RFC.

The designer could have made a mistake though and specified heaters that do store some water. In this case, the OSG's guidance is that diversity cannot not be applied. 2 x 32A RFCs would be required.

 

[cliffed]

Thanks.

 

[Toneyz]

For all the schools we have done the consultants have always designed on radials.

 

[cliffed]

For all the schools we have done the consultants have always designed on radials.

Agree,really can’t see the point of this circuit.
It’s ridiculous,the tpn DB installed is a 6 way ie:18 circuits,the number of circuits on the drawing relates to 14 circuits,there are already a couple of extra circuits to be added,this all specified by consultants,kinda mad mad mad

 

[TJ Anderson]

Are they instantaneous or stored water type?

Depending where they are positioned in that ring could mean that one leg is being overloaded.
3kW fixed loads is not a good idea on a ring. They would have to be fused spurs with fuses running at limit, although you could probably argue load is determined and fit DP switches.

 

[TJ Anderson]

Ask to see designers calcs!

 

[cliffed]

Cheers to all,will look @heaters Monday to find what they are,& will question the design.

 

[davesparks]

Just because they can do it, and probably justify it by calculation, doesn't mean that it is the best way to do it.

 

[cliffed]

Always radials back to DB for me,other sparkies on site,attitude just do what’s on drawing.
That applies to everything including guessing positions on rooms,without asking for a detailed drawing,then when 2nd fix comes a knocking,it’s all wrong,& blamed on me.