Economy 7 wiring

[Paulmcfadyen]

Looking for the expert opinions of you guys. My first floor flat has an Economy 7 setup, with everything on the constant supply except for the one 2.55 kW storage heater and one 3 kW immersion heater, connected to the timed supply via a 2-way CU. I've acquired an additional 1.7 kW storage heater and am about to connect it up with the other timed appliances via a new, larger timed supply CU. So far so good, however the timed CU supply seems to be wired in 6 mm cable! May even be 4 mm but I think this is unlikely? It's about 10 metres from the main meter room. Block built around 1980. Am I within the limits of this supply cable to connect the additional heater? If not, the new heater could go into the constant CU with some sort of timer to switch it on during off-peak times only? What equipment do you recommend to sense the off-peak coming on and energise the new heater if I go down this route?

 

[Lectrician]

Look at the fuse at the origin in the meter room. Is it only a 30 or 45amp sw fuse??

I have seen setups like this, very undersized. But it is due to the fact that there is a small REC supply feeding several flats.

 

[Paulmcfadyen]

I admit that I've never explored in much detail. Would this be within the same unit as the main switchfuse for the constant supply? There's only one switch on that box...

 

[Lectrician]

Na, two seperate units.

Prop a larger 60amp, and a smaller 32 or 45.

Sounds very familiar that set up, golf wouldn't mean anything would it?

 

[Paulmcfadyen]

Golf???

I'll have a look in the meter room and see what I can discover.

If this is 6 mm cable, am I OK to add the extra heater as described?

Cheers.

 

[kai]

The 6mm cable cannot support an immersion and Two Storage Heaters, the cable must be 10.0.sq.mm. or above, depending on method of installation, and length of run.

13amps times three gives 39amps, the 6mm cable takes 38amps.

 

[Paulmcfadyen]

My calculation was:

3000 + 2550 + 1700 = 7250 W

divided by 240 V (Which all 3 are rated at)

= 30.21 A.

So much less than the maximum 38 A.

Have I made a mistake then?

 

[andy]

My calculation was:

3000 + 2550 + 1700 = 7250 W

divided by 240 V (Which all 3 are rated at)

= 30.21 A.

So much less than the maximum 38 A.

Have I made a mistake then?

use 230V for all calculations

 

[plugwash]

yeah the 6mm tails will take your current planned addition

but if the new CU is bigger then there is temptation to add even more to it. Therefore i would stronly suggest replacing the old 6mm tails at the same time.

 

[Paulmcfadyen]

Using 230 V gives 31.5 A

The tails go through walls, below the floor and through the cavity wall of the flat below to the meter room. It'd be a HUGE job to replace them, if not totally impossible! Otherwise, I would!

 

[plugwash]

is there any overcurrent protection for theese tails in the meter room

if not then i would put a 45A switchfuse in them in the meter room.