Spurs off a ring

[Justin Passing]

I need supplies for 2 x immersion heaters, a boiler and a pump.
I can get to the ring (for the floor) but can't get the ring cable to where the FCUs need to be mounted.
Can I use junction boxes to take spurs off the ring like this,

or is there a better way to do it? Should I extend the ring - using 2 junction boxes to join a piece of cable in?
There's no way to get new cables back to the consumer unit.
Thanks

 

[HullMarc]

The way you plan to put it together is fine (as long as the JBs are accessible), but the idea of having 2 immersion heaters on a ring? What's their rating (usually 16a), and what else is on the ring?

 

[LoveRocket]

I need supplies for 2 x immersion heaters, a boiler and a pump.
I can get to the ring (for the floor) but can't get the ring cable to where the FCUs need to be mounted.
Can I use junction boxes to take spurs off the ring like this,

or is there a better way to do it? Should I extend the ring - using 2 junction boxes to join a piece of cable in?
There's no way to get new cables back to the consumer unit.
Thanks

That is a terrible, terrible design.

The regs recommend that any fixed load over 2kW should have its own dedicated circuit.

I'm guessing your immersions are 3kW, which is bang on the limit of 13a. Having an immersion heater on a ring is bad, having two of them on the same ring is awful.

With your layout (even if you extended the ring), there is a very real chance that you could overload one leg of the ring.

 

[echoes]

Your 5A FCU for boiler is OK, but you have a spur-off-a-spur for your pump FCU which is not allowed ("Each spur may serve only one socket outlet or fused connection."), despite both being fused at 5A - I'll defer to the pros about this.

Usually immersion heater is supplied by a dedicated 15/16 A radial circuit; one on a ring would be OK but not ideal. But 2, if both 'on', would consume (close to) the ring's rated current carrying capacity. Rings are not designed for this. Is there no way can you run a separate cct(s) to you immersions?

Immersions aside, you may use JB's to spur off a ring like this, provided the JB's are 'accessible' and the number of spurs does not exceed the number of sockets on the ring.

EDIT: The gents above beat me to it!

 

[ericmark]

For boiler and pump yes but for immersion heaters no. The limit is 2000W for a fixed appliance after which it needs it's own dedicated supply.
You are allowed 3 meters of cable from point it spurs from to fuse.

There is also now requirement that all cable less than 50mm from surface and buried in wall or floor is protected either using special cable like Ali-tube or with a RCD.

However DIY sheds don't sell Ali-tube cable and whole sale want you to buy a role so works out expensive.

And of course it will all need inspecting and testing and unless you have the test gear that's also not easy. Even to hire is expensive. Three meters normally needed and I found a price to hire one at £44 per week plus £30 carriage so must be looking at around £100 min for all three.

To buy around the £750 mark can't really see as cost effective.

 

[londonboy]

Why cant you get cables back to the CU? Its rarely impossible!

In this situation I'd probably suggest putting a 5way CU in the boiler cupboard and running an armoured/etc up from the existing CU.

Could you run externally? Conduit etc?

 

[flameport]

Two large loads at the same point on the ring = poor design

Two immersion heaters on a ring = just asking for the MCB to trip often.

Two spurs from one cable = not allowed, regardless of what fuse you might put in them.

Boiler supplies usually have 3A fuses anyway.

Summary - the proposed design is a shoddy mess.
The only correct solution is one or more new circuits from the consumer unit.
There must be a way to get cables there - someone managed to get the existing ring cables in.

 

[OwainDIYer]

Boiler and pump should be supplied through the same FCU so the entire CH/HW system can be isolated at one point.

Two immersion heaters on the same circuit is a very bad idea.

 

[Justin Passing]

Thanks all.

someone managed to get the existing ring cables in.

Yeah then it got built over! CU is 2 floors down.

So it's one Immersion ( it's only for backup), and separate spurs for the boiler and pump. (shower not boiler pump). Currently they're just plugged in to sockets.

 

[holmslaw]

..

 

[echoes]

So it's one Immersion ( it's only for backup)

Seems odd to originally plan for 2 backup immersions . It's still a bad design.

 

[Steve]

separate spurs for the boiler. Currently they're just plugged in to sockets.

Assuming this is a central heating boiler it can't just be plugged into any old socket. It has to be a socket taken off of the central heating wiring.

¿que?

Yes, a system boiler would need wiring to the system wiring centre, such that it is on when the system calls for heat. The wiring centre can recieve power from a plug and socket.

A combi can just be plugged into any socket. But best practice is to provide a seperate circuit for heating nowadays.

 

[holmslaw]

..

 

[Steve]

All central heating wiring should emanate from a common point so that isolation at that point makes the whiole system safe.

Did I say otherwise? . . .

Yes, a system boiler would need wiring to the system wiring centre

One throw of a switch or removal of a plug would render the system dead, since all components are wired from the wiring centre....

A combi can just be plugged into any socket

Because the combi takes the place of all the individual components of the system, and thus only requires individual isolation. Yes there may be a thermostat somewhere, but this is always wired from the boiler....

So what the f*** are you talking about oh one of little knowledge and common sense but many posts.

What have I done wrong to deserve this? Have I said something to offend you?

Do you do electrical work for a living?

You know full well. But the answer matters not IMO.

 

[ColJack]

nevermind..