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Discussion Starter · #1 ·
Hi all,

I have ordered an Etron on lease , which includes free installation of a pod point charger. The whole leasing and ordering process has taken much longer than I anticipated ... but the charger install is booked for the week after next. I am slightly worried (perhaps paranoid!) that the charger installation won't be straightfoward and I will end up having to cancel - which leaves me either car less or needing to MOT and insure my existing car unnecessarily while I start looking for an alternative new ICE car.

I know there can be issues when the main fuse is 60A... I had thought mine was 80A based on visual inspection of the meter box (See pic and fuse labelled 80A). However, we had a new consumer unit fitted last year and I notice the electrical install certificate seems to show the maximum load to the property is 60A. Can anyone shed any light on this? Is it likely to be an issue ?

I have sent all this to pod point and they have scheduled the install so I assume they are happy, but the person I spoke to on the phone didn't fill me with confidence (giving the impression they had hadn't looked at the pics/certficate I had sent)

Any help / advice appreciated!
 

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That's a 100 A fuseholder fitted with an 80 A fuse, so you should be fine. Looks like someone made an error when doing the EIC. FWIW the incoming cable is 35mm² concentric so good for over 100 A, so, depending on the local LV distribution network capacity you might be able to get the DNO to put a 100 A fuse in place of the 80 A one fitted, if it was an issue.
 

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Discussion Starter · #3 ·
That's a 100 A fuseholder fitted with an 80 A fuse, so you should be fine. Looks like someone made an error when doing the EIC. FWIW the incoming cable is 35mm² concentric so good for over 100 A, so, depending on the local LV distribution network capacity you might be able to get the DNO to put a 100 A fuse in place of the 80 A one fitted, if it was an issue.
Thanks - so should be fine?. Forgot to mention that the meter is new (we had it moved last year due to some work we had done on the house). Would 100A fuse offer any advantages over 80A? (I can't find much online about how suitable an 80A fuse is). The charger is 7KW - and the etron has a big battery so don't want pod point to downrate the charger to 3.5KW.

I queried the info on the certificate with the person who called to scheduled the install and they suggested that the 'maximum load' to the property may be 60A... It sounds like you are saying that is unlikely?

Thanks again for advice
 

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Thanks - so should be fine?. Forgot to mention that the meter is new (we had it moved last year due to some work we had done on the house). Would 100A fuse offer any advantages over 80A? (I can't find much online about how suitable an 80A fuse is). The charger is 7KW - and the etron has a big battery so don't want pod point to downrate the charger to 3.5KW.

I queried the info on the certificate with the person who called to scheduled the install and they suggested that the 'maximum load' to the property may be 60A... It sounds like you are saying that is unlikely?

Thanks again for advice
It's just an error in Part 6 of the EIC, perhaps the person doing the work misread the label, as the fuse fitted is clearly marked as being 80 A, and it is a BS1361 Type 2. As the fuse is sealed and there are two isolation switches the electrician could use for safe isolation when fitting the CU, then he/she would have had no need to get the main fuse pulled to do the work, and without pulling that it's not possible to confirm the fuse rating. You're lucky that someone has stuck a label on giving the fuse rating, as most don't have this and it then means the fuse has to be pulled to read the value. Always a good idea to label the fuse holder with the actual fitted fuse rating like this.

I can't say what your maximum demand is, that needs a physical look at the installation and all the loads, plus an assessment as to how diversity may apply to those loads. My guess is that the figure of 60 A in Part 7 is just an estimate made by the person fitting the CU, not a measured value. It would be unusual to actually measure the demand when fitting a CU, almost always it's just an estimate, and probably one that conservative.

There is a way to do this using the diversity guidance in the On Site Guide to BS7671:2018, and if you take a photo of the CU, showing the number of circuits and their ratings, I could quickly give a rough estimate, but to do a reasonable job needs knowledge of the actual ratings of high current appliances, like cookers, hobs, water heaters, etc.
 

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Discussion Starter · #5 ·
It's just an error in Part 6 of the EIC, perhaps the person doing the work misread the label, as the fuse fitted is clearly marked as being 80 A, and it is a BS1361 Type 2. As the fuse is sealed and there are two isolation switches the electrician could use for safe isolation when fitting the CU, then he/she would have had no need to get the main fuse pulled to do the work, and without pulling that it's not possible to confirm the fuse rating. You're lucky that someone has stuck a label on giving the fuse rating, as most don't have this and it then means the fuse has to be pulled to read the value. Always a good idea to label the fuse holder with the actual fitted fuse rating like this.

I can't say what your maximum demand is, that needs a physical look at the installation and all the loads, plus an assessment as to how diversity may apply to those loads. My guess is that the figure of 60 A in Part 7 is just an estimate made by the person fitting the CU, not a measured value. It would be unusual to actually measure the demand when fitting a CU, almost always it's just an estimate, and probably one that conservative.

There is a way to do this using the diversity guidance in the On Site Guide to BS7671:2018, and if you take a photo of the CU, showing the number of circuits and their ratings, I could quickly give a rough estimate, but to do a reasonable job needs knowledge of the actual ratings of high current appliances, like cookers, hobs, water heaters, etc.

Thanks - yes it makes sense that it is just an estimate... or perhaps the old meter had a 60A fuse before being moved?? (it was moved around the same time as the new CU was fitted - I cant recall which happened first).

Thank you for your help - it's sounding like it should be fine. I have attached pics of fuse board, if there is a quick way to work out if I would have any probs that would be great, but no worries if not. I guess i will find out either way soon enough!!
 

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Just using the normal diversity rules in Appendix A of the OSG, without actually looking at the number of outlets and the ratings of things like the cooker and boiler is going to over-estimate your total demand, as you have an unusually high number of socket circuits. My guess is that this is why the installer chose 60 A, probably as a WAG, as following the OSG diversity rules, using the MCB ratings as the max per circuit (which is an over-estimate for sure) gives a total demand of over 140 A, which is clearly bonkers.

The diversity rules are only guidance, though, and are really for things like MCB and cable sizing, rather than working out total demand. For anyone interested, they are in the tables copied below:

145539


145540


If I were estimating total demand on your installation then I'd be inclined to just fit a monitoring clamp meter to the tails for a few days and record the peak demand. My guess is that it probably won't exceed about 30 to 40 A in reality, as it looks as if the reason you have so many socket circuits is probably due to the way the house has been changed over the years, and that if it were to be wired from scratch now the number would almost certainly be lower.

In all probability the install will be fine. Worst case may be that they request the DNO change the fuse for a 100 A one, but more often than not that isn't a problem, especially given that the incomer looks to be fairly modern (well, not more than 30 or 40 years old at a guess, and that counts as modern as far as the LV network goes).
 

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Discussion Starter · #7 ·
Hi - thanks for this. Yes we had an extension and the new sockets were wired on a separate circuit. I don't think we have an abnormally large number of sockets (in fact in the original parts of the house the number of sockets/room is a bit measly). Cooker and boiler are new and selected to be energy efficient (not sure if that effects the rating). No electric shower, or other high demand appliances as far as I know.

Blimey it's not straightforward is it - I have gone from sceptical to optimistic back to sceptical. Maybe the best I can do is cross my fingers and hope we get a good installer who knows what he is doing!!

Thanks a lot for your help (y)(y)(y)
 

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I think you'll be fine, as I really doubt that your demand is as high as the 60 A estimate on that EIC. Our house is all-electric, electric heating, hot water heating etc, with no other fuel. Our maximum demand in winter is normally only around 30 A or so, with the heating and hot water on at the same time. The hob and oven can draw around 30 A if both are on, but only for a short time, and because our heating and hot water both run over night during the off-peak period we never have both these loads on at the same time. We have two charge points installed, at either end of the drive (we have two EVs) and could easily run both of them and still have spare capacity from the 100 A fused supply we have.

The guidance in the OSG is very conservative in practice, which is why I think that it makes sense to actually measure the load over a period of time to get a much better feel for the true figure if there's any suspicion that demand might be a bit high (which I really don't think is the case for your installation). Not hard to do, and the DNOs have small line monitors they can temporarily connect to log data over a period of a week to see the maximum and mean. It's the mean that matters, as an 80 A fuse won't blow at 80 A, it needs a heck of a lot more current to blow it fairly quickly.
 
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