Checking installation methods of RFC

[hightower]

Hi all,

Been asked to installed some sockets in our sports hall. These are to power 4x 3kW blow heaters (yes, I know little blow heaters aren't the most efficient method of heating a large room like this, I've made my arguments and may be given the budget to do a proper IR heater install in future, but this is just a short term fix for now).

Anyhow, I was originally thinking 4x 16A radials would be best, each supplying a single socket. Then I thought perhaps 2x 32A RFCs would be more adaptable in the future if I need to pull more sockets off for another purpose.

My plan is steel conduit, singles, 32A type B RCBO, each RFC feeding 2 sockets. The furthest socket will be around 20-25m away from the board.

I'm just undecided - 2x RFCs, or 4x radials. What do people think?

 

[Pete999]

Hi all,

Been asked to installed some sockets in our sports hall. These are to power 4x 3kW blow heaters (yes, I know little blow heaters aren't the most efficient method of heating a large room like this, I've made my arguments and may be given the budget to do a proper IR heater install in future, but this is just a short term fix for now).

Anyhow, I was originally thinking 4x 16A radials would be best, each supplying a single socket. Then I thought perhaps 2x 32A RFCs would be more adaptable in the future if I need to pull more sockets off for another purpose.

My plan is steel conduit, singles, 32A type B RCBO, each RFC feeding 2 sockets. The furthest socket will be around 20-25m away from the board.

I'm just undecided - 2x RFCs, or 4x radials. What do people think?

HT 4 Radials Mate.

 

[SparkyChick]

I might be inclined to install them as 16A radials powering a single socket. Run two circuits in one conduit and include an extra set of singles between the two sockets so you can convert to a ring if needed at a later stage without the hassle of pulling in new cables.

 

[hightower]

I might be inclined to install them as 16A radials powering a single socket. Run two circuits in one conduit and include an extra set of singles between the two sockets so you can convert to a ring if needed at a later stage without the hassle of pulling in new cables.

Those cables would then need tying to earth somehow though. But I like your thinking. 4x 16A radials it is. I liked the convenience of a ring but one of first things I saw when looking in Appendix 15 was 'not supplying comprehensive space heating', so RFC out then.

Cable calcs say 2.5mm cable is alright, table in OSG says 40m max run (which is fine), space in the board for the 4 RCBOs, conduit will gladly take 6x 2.5mm cables. We may have a winner.

 

[SparkyChick]

Earthing... no problem... slim-line 5 way Wago at one end of the spares tied into the earthing

 

[telectrix]

should you not link to E at both ends, saves having ends flapping about.

 

[SparkyChick]

should you not link to E at both ends, saves having ends flapping about.

Bit of tape, fold them over into a loop and stuff the ends back up the pipe?

 

[SparkyChick]

I'm being a bit flippant because it's more interesting than what I have to do this morning... remove some existing RFC cabling and replace it, hopefully finding a chunk taken out of the cable that would explain the crappy IR readings on the two cable segments I'm replacing.

 

[hightower]

I'm loving my workload at the minute, it's got me thinking about all the stuff I've learned about over the years. Beats doing a typical house rewire where the boss says "just drop a 10mm in for the shower".

Now I'm thinking do I drop 4mm in or am I happy with 2.5mm. The calcs all check out for 2.5mm but I'm just thinking if I need to extend in the future for some reason.

 

[Toneyz]

I'm loving my workload at the minute, it's got me thinking about all the stuff I've learned about over the years. Beats doing a typical house rewire where the boss says "just drop a 10mm in for the shower".

Now I'm thinking do I drop 4mm in or am I happy with 2.5mm. The calcs all check out for 2.5mm but I'm just thinking if I need to extend in the future for some reason.

Don't overthink it, it is 4 radials for 4 heaters unless you are thinking of what the correct way of heating the hall is (maybe in the future).What was your calculation for heating the hall correctly also how is the temperature being controlled eg roomstat.

 

[hightower]

I haven't done any calculations for heating the hall yet, that'll come when someone says "aye, stick some proper heating in"

 

[Toneyz]

Is there not some form of existing heating or has it had its day?

 

[Deleted member 72666]

I'm assuming you're not going to use BS1363 sockets to supply these heaters because if you are you'll be back time and time again replacing the charred plugs and sockets. 16a 2p+e to BS4343 would be my choice if not using fcu's.

 

[telectrix]

or a 20A D/P switch (neon optional).assuming that the flex to the haters is rated to 16A or above).

 

[hightower]

Don't want the heaters hard wired due to it being a sports hall. I'm sure I'll get funding to do the job properly with suspended IR heaters eventually, but yes, this is a short-term fix and although not ideal it will help us to get through 3 weeks of exams starting Monday.

 

[Leesparkykent]

2 radials.

 

[Adam W]

Don't want the heaters hard wired due to it being a sports hall.

What is the reasoning behind this? I'd have gone for 2x rings with the heaters on FCUs.
If it's only going to be temporary a diesel or propane heater will chuck out a lot more heat than small fan heaters.

Or is it a trick question, ie you don't need heating at the moment?

 

[Pete999]

What is the reasoning behind this? I'd have gone for 2x rings with the heaters on FCUs.
If it's only going to be temporary a diesel or propane heater will chuck out a lot more heat than small fan heaters.

Or is it a trick question, ie you don't need heating at the moment?

Think of the amount of callouts if you fitted these heaters on a 13 A fcu
3000W /230 =13.04A mps wouldn't take long to blow those would it, an why Ring Final, what's the point? plus the BS 7671 RECOMENDS that a fixed load of plus 2KW would be better on a dedicated circuit.

 

[Adam W]

Think of the amount of callouts if you fitted these heaters on a 13 A fcu
3000W /230 =13.04A mps wouldn't take long to blow those would it, an why Ring Final, what's the point? plus the BS 7671 RECOMENDS that a fixed load of plus 2KW would be better on a dedicated circuit.

Maybe, but 3000/240 = 12.5, 240v being more like what you actually get in the UK. 2x2.5mm are easier to terminate than 2x4mm. If the ring only consisted of FCUs supplying heaters then that would make it a "dedicated circuit" would it not?

 

[Pete999]

Maybe, but 3000/240 = 12.5, 240v being more like what you actually get in the UK. 2x2.5mm are easier to terminate than 2x4mm. If the ring only consisted of FCUs supplying heaters then that would make it a "dedicated circuit" would it not?

It could well do until some idiot come along and sees it's RFC and starts adding 13Amp socket all over the shop, not realising it's a dedicated circuit for heaters.

 

[hightower]

Why would there be 2x4mm @Adam W ? I'm running dedicated radials, 16A breaker, single socket (for a single 13A appliance), 1x2.5mm.

As for the FCU question, I'd have thought it would have been obvious from the information I've posted already. This is a sports hall. Having blow heaters lying around the floor when little Johnny is playing footy isn't going to be very useful. On plugs, they can plug them in when the room is due to be used for exams, unplug them when due to be used for sports.

 

[hightower]

Maybe, but 3000/240 = 12.5, 240v being more like what you actually get in the UK. 2x2.5mm are easier to terminate than 2x4mm. If the ring only consisted of FCUs supplying heaters then that would make it a "dedicated circuit" would it not?

Hmmm good point, thanks. Remind me, what reg is it that says we're allowed to design by 240v again? I forget.

 

[Pete999]

Nice

Hmmm good point, thanks. Remind me, what reg is it that says we're allowed to design by 240v again? I forget.

HT nice

 

[Adam W]

I thought you were asking for suggestions.

 

[ipf]

Think of the amount of callouts if you fitted these heaters on a 13 A fcu
3000W /230 =13.04A mps wouldn't take long to blow those would it, an why Ring Final, what's the point? plus the BS 7671 RECOMENDS that a fixed load of plus 2KW would be better on a dedicated circuit.

They would take a bit of 'blowing' but, from what I've seen, the plug/sockets would be giving a fair bit of heat off.
One place has one on a 4mm radial (a couple of other sockets involved) no fuse problems but a lot of heat at the plug....it worries them a bit.
What surprises me about these 3kw heaters is that some do come with a 13amp plug top fitted.
If you're looking to future additions, maybe 4mm2, DP switches.

 

[ipf]

They would take a bit of 'blowing' but, from what I've seen, the plug/sockets would be giving a fair bit of heat off.
One place has one on a 4mm radial (a couple of other sockets involved) no fuse problems but a lot of heat at the plug....it worries them a bit.
What surprises me about these 3kw heaters is that some do come with a 13amp plug top fitted.
If you're looking to future additions, maybe 4mm2, 20amp DP switches.

 

[Adam W]

Nice

HT nice

Perhaps you'd care to explain that one then Pete?
How is asking for suggestions and then making sarcastic jabs when people do suggest things "nice"?

 

[hightower]

I thought you were asking for suggestions.

I am mate, but I would prefer it if the suggestions complied with the rule book.

 

[Risteard]

A ring final circuit serving two single socket outlets seems daft to me.

 

[Flanders]

As others have said i would go for 16 amp sockets id go for the gwis switched interlock ones as they can take a good bashing from them pesky kids

 

[Adam W]

A ring final circuit serving two single socket outlets seems daft to me.

I'm not too sure what OP means by "blow heaters" - I took that to mean some kind of fan heater; turns out he wants to put free-standing heaters on the floor which can be cleared away so they don't get knocked over. I would have been more inclined to use 3x 2400W (probably infra red) heaters at high(ish) level per ring, x2. I've done this before and nothing burned out since the heaters were designed to work through a 13A fuse.
It seems he's intent on going for individual 16A radials wired in conduit as a temporary measure for 3 weeks at a time when heating may not even be required at all.

If any alterations are going to be made to this setup it's likely to be that the commando sockets are changed for BS1363 to make them more flexible, eg so the cleaner can plug in a floor polisher or vacuum cleaner, whereas hard-wiring everything permanently makes it more of a 'dedicated circuit'.

The whole thing seems daft to me.

 

[Adam W]

I am mate, but I would prefer it if the suggestions complied with the rule book.

Meaning what exactly? Where does BS7671 give a value of nominal voltage as 230V, or for that matter any figure other than low voltage "Exceeding extra low voltage but not exceeding 1000Vac or 1500Vdc between conductors, or 600Vac or 900Vdc between conductors and earth"?
Have you actually measured the voltage in this sports hall of yours or are you just going to guess?

 

[Ian1981]

It’s very difficult to design a circuit to a voltage that can vary so using 230 v and designing to this voltage for calculating loads and volt drop gives us a good safety margin to design too I find.
That said some manufacturers put 240 v on the information plates so in that case I use that.

 

[Toneyz]

See appendix 2 from 1995 230v is the nominal voltage that tables and calculations are worked out from.