Maximum demand on EICR

It's been on EICs for ages ... presumably to demonstrate that the supply is suitable for the installation - I suppose it makes sense to re-validate that assumption on an EICR as extra loads may have been added over time?

   - Andy.

AJJewsbury said:

I suppose it makes sense to re-validate that assumption on an EICR as extra loads may have been added over time?

Surely determining MD for the installation is the purvey of the Designer?

During an EICR, especially for non-domestic or a complex installation, how can the MD actually be 're-validated' ?

AJJewsbury said:

as extra loads may have been added over time?

It's necessary for the designer to do this as part of additions and alterations.

AJJewsbury said:

I suppose it makes sense to re-validate that assumption on an EICR as extra loads may have been added over time?

Surely determining MD for the installation is the purvey of the Designer?

During an EICR, especially for non-domestic or a complex installation, how can the MD actually be 're-validated' ?

AJJewsbury said:

as extra loads may have been added over time?

It's necessary for the designer to do this as part of additions and alterations.

In reality, does anyone do anything other than write down the rating of the supply fuse?

I doubt it, but how do you know its rating without having a look?

Even if there is a 100 A fuse, the agreed after diversity maximum demand may well be lower than 23 kVA.

gkenyon said:

It's necessary for the designer to do this as part of additions and alterations.

But isn't half the point of a periodic inspection to catch the things that perhaps haven't been done properly - we don't just look for degradations due to the passage of time, but simple non-compliances too?

During an EICR, especially for non-domestic or a complex installation, how can the MD actually be 're-validated' ?

The forms are only intended for simple 100A and below installations, and are only models at that, so people are free to omit that section on large/complex installations if they feel it serves no purpose. For a domestic a nudge to check that three 10kW instantaneous showers on a 60A DNO fuse might not be a good idea is worth consideration I would have thought. As for the mechanics, tot up the loads (circuits/floor areas for small plug in loads), apply diversity and a bit of common sense  - same as the designer should have done in the first place. Significant new loads are becoming if anything more common (EV, Heatpumps, instantaneous showers) and the DIY community certainly hasn't gone away.

   - Andy.

AJJewsbury said:

The forms are only intended for simple 100A and below installations, and are only models at that, so people are free to omit that section on large/complex installations if they feel it serves no purpose. For a domestic a nudge to check that three 10kW instantaneous showers on a 60A DNO fuse might not be a good idea is worth consideration I would have thought.

Agreed, although that doesn't mean the person carrying out the EICR has to re-assess the MD - just note that the rating of the fuse is going to be exceeded, or question the overall MD?

AJJewsbury said:

For a domestic a nudge to check that three 10kW instantaneous showers on a 60A DNO fuse might not be a good idea is worth consideration I would have thought.

And ask the home owner if they've had any nuisance trips, perhaps recently. E.g. Those half price electric Sunday afternoons from Scottish/British Gas (avoids reductions in gas use..).

We had some trips when the washing machine, dish washer and kettle all ran at the same time on a B16 breaker (all the dirties saved up for the cheap rate period). Similar 'mis-design' issue made worse by external changes.

The circuit has now been split and the washing machine leg is on a lower likely consumption circuit.

Philip Oakley said:

We had some trips when the washing machine, dish washer and kettle all ran at the same time on a B16 breaker (all the dirties saved up for the cheap rate period). Similar 'mis-design' issue made worse by external changes.

I might expect that the kettle's contribution would be covered by diversity.

The dishwasher and clothes washer aren't exactly heating the water for a sustained period.

However, let's say 2 kW each = 26 A. Figure 3A4 suggests that you might get between 200 s and 400 s before tripping.

I must say that with less than 50 p savings per Sunday, I found that the inconvenience was not worth it.

Chris Pearson said:

I must say that with less than 50 p savings per Sunday, I found that the inconvenience was not worth it.

Yes, but, as the financial controller says "we're doing it anyway"..

You are right that the savings don't count to much, though it will matter to some, and it can lead toward overload.

I was mainly pointing out that the trick of "you could always ask" can give clues as to changes in usage for maximum demand (overall and per circuit). And the possibility of useful extra work.

Chris Pearson said:

The dishwasher and clothes washer aren't exactly heating the water for a sustained period.

They wouldn't need to be, especially with the kettle.

Most UK washing machine heating elements are indeed around 2 kW, many kettles 3 kW, but the washing machine motor and dishwasher recirculation pump are often going at the same time ... potentially looking at over 7 kW there if everything is heating at the same time. 

16 A circuits for white goods should be a single appliance per breaker really. 20 A, perhaps two appliances per circuit, but I wouldn't do that if one of the appliances were a tumble dryer.

gkenyon said:

16 A circuits for white goods should be a single appliance per breaker really.

Agreed, although your double socket-outlet in the scullery is just crying out for a washing machine and tumble drier. Even on a 32 A breaker, the socket may be overloaded at times.

That's the joy of old houses! Historic ring circuits no longer being complete after kitchen remodelling maybe 20 years ago..