Maximum demand and EVCP's

[HappyHippyDad]

I'm always in a dilemma with regards max demand. Often you work it out and it's higher than the the 80A or 60A cut out fuse. However, you know that in reality it is absolutely fine.

I have thought about this in the past when installing electric showers. Now with EVCP's as well it's making me think a bit harder!

The DNO around here will only allow an 80A fuse if meter is inside. Let's give an example of a standard house.

Shower 40A
Cooker 32A
Sockets 32A
Sockets 32A
Garage 16A
Boiler 16A
Lights 6A
Lights 6A

With the osg diversity (which I rarely use for total demand of house hold), you nearly always get >80A. With the 40% rule in the above example you get 72A which is more realistic, but still leaves no room for a 7.4kW EVCP.

Would you fit one anyway, knowing it will be ok?
What would you guys do realistically?
@Gavin John Hyde , you must come across this lots. I realise there is the CT clamp option, but in this standard example is it really necessary?

 

[Mikegh]

I'll take a guess

If it's strictly off-peak it's ok.

It mostly is but not strictly off-peak so you'll need some type of interlock or throttling of the car charging

Don't see any way round it

 

[Gavin John Hyde]

I'm always in a dilemma with regards max demand. Often you work it out and it's higher than the the 80A or 60A cut out fuse. However, you know that in reality it is absolutely fine.

I have thought about this in the past when installing electric showers. Now with EVCP's as well it's making me think a bit harder!

The DNO around here will only allow an 80A fuse if meter is inside. Let's give an example of a standard house.

Shower 40A
Cooker 32A
Sockets 32A
Sockets 32A
Garage 16A
Boiler 16A
Lights 6A
Lights 6A

With the osg diversity (which I rarely use for total demand of house hold), you nearly always get >80A. With the 40% rule in the above example you get 72A which is more realistic, but still leaves no room for a 7.4kW EVCP.

Would you fit one anyway, knowing it will be ok?
What would you guys do realistically?
@Gavin John Hyde , you must come across this lots. I realise there is the CT clamp option, but in this standard example is it really necessary?

With the new DNO form you are 90% of time going to have to submit your ema form pre install anyway. WPD will send you a pre works letter or email saying go ahead or we are changing cut out.
In this scenario i include covering letter and images of the mcbs. The planners like this and I explain that calculated MD vs real life MD is completely different. They get this and normally say go ahead if its and 80+ amp supply. My experience is DNO only get twitchy if its a 60a or looped supply.

 

[Gavin John Hyde]

With the new DNO form you are 90% of time going to have to submit your ema form pre install anyway. WPD will send you a pre works letter or email saying go ahead or we are changing cut out.
In this scenario i include covering letter and images of the mcbs. The planners like this and I explain that calculated MD vs real life MD is completely different. They get this and normally say go ahead if its and 80+ amp supply. My experience is DNO only get twitchy if its a 60a or looped supply.

When talking to the planners at WPD they said in calculating MD they typically ignore lighting unless it has significant number of.fittings. when you think about it though it makes sense as so much stuff now is ac to dc via adaptors. And lights are led. My new oven uses a 13amp plug albeit.coming off a 10mm/40amp circuit... So the md calculations are not very reflective of real life

 

[Mikegh]

How do you calculate demand in the UK

100% immersion
100% shower
100% water heater
100% evcp
Sockets 100% largest appliance +40% of each other large appliance
Cooker 10A +30% remainder

Add them all up and ignore lighting, figure for other appliances seems too high at 40%

Calculating off mcbs seems like a waste of time , figure could be way off

 

[newfutile]

Some evcp,s have current transformers and you can set the cut out fuse so that its never exceeded ,mcbs ratings are useless as they don’t always reflect design current .