Distribution board has 63A fuse and ESB fuse is 80A. How do I utilise the extra 17A

KCross · 14-11-2016 11:10pm #1

I have the "increased supply" (16kVA) from ESB Networks and they have confirmed to me that the fuse on the ESB side of the meter is an 80A fuse. I believe the standard fuse is a 60A fuse (12kVA supply).

The main fuse on the distribution boards is rated 63A
I have a few electric hungry devices, the two main ones being:

- Heat Pump
- Electric Car

The heat pump runs at 22.5A (it takes more starting current but it has a soft starter) and the car runs at 32A and they run daily at the same time (during night rate electricity). The car, in particular, draws a constant 32A for several hours every day. The heat pump cuts in/out as it sees fit so its "on time" is variable but they do run at the same time at least once a day.

Add in a few other devices and I am close to the main distribution board fuse which is, by default, 63A is every house.

So, my question, to all those RECI certified electricians out there is what is allowed, from a domestic regulation perspective, to "unlock" the extra 17A between 63A(on the board) and 80A(in the meter box)?

Example: Can I simply take the 40A C-Type RCBO on the distribution board that controls the car charger and wire it outside the main 63A fuse on the board? i.e. connect it direct to the supply coming into the distribution board or do I have to wire a second distribution board or what other options are there?

Note: I dont want to go down the route of priority switches. I want to utilise the 80A. I paid for it so I want to use it.

I am obviously not planning on doing this myself. I will be getting a certified electrician to do it but I want to hear what my options are before I get someone out.

The house was built in 2011 and the tails were upgraded to allow for the increased supply so I should be able to draw the 80A without burning the house down!

thanks
KCross

15-11-2016 12:22am

Has the main fuse ever blown?

Tuco88 · 15-11-2016 12:23am

It's there for good fuse discrimination, you will not be able to "tap into" into it, we'll you shouldn't and it would be very poor practice to to so.

In the event of a fault or overload you will want your 63amp mcb or fuse to trip.Allowing you to fix or reset the problem. If the 80amp goes the ESB will have to be called and paid for ,and will want to know why it happened.

You will need to look at your incomer, I'm not sure if a 100 amp supply is available.

KCross · 15-11-2016 12:56am

@2011, no it hasn't blown but I don't have the car long (a few months) and the heat pump is going to be running more with the winter coming so I'm thinking it's a possibility. Would rather get ahead of it if possible.

@tuco88, I must be missing something then. If a standard connection (12kVA) with a 60A ESB fuse is the normal, what use is the increased supply (16kVA-80A) if all I can do is still just go to 60A like everyone else? The form I filled in when requesting the connection said a continuous 70A was allowed on the supply. Your response doesn't make sense to me. Can you explain what the increased supply has given me?

Tuco88 · 15-11-2016 1:20am

With a 12kva mic supply, A consumer unit will have a 50 amp followed by the ESB 63/60 amp fuse. For discrimination tails protection so on.

With a 16 kva mic supply, A consumer unit will have a 63amp followed by the ESB 80amp.

There is a 20 kva mic available and a 29 kva single phase mic available also if I remember thats a 100/125 amp ESB fuse.

Your 63amp fuse/mcb won't blow/operate at 63amps on the button it will draw more current depending on fuse/mcb characteristics.

Have you measured the loads accurately?

KCross · 15-11-2016 2:07am

Ok, I misunderstood the rating on the fuse board of a standard connection then. I thought everyone had a 63A fuse. Apparently not.

In relation to measuring the load, I know the car charger is drawing 6.6kW. The car shows me that being drawn and I have also got a kWh meter attached to it so I know that's right. It draws that power continuously.

The heat pump draws various power levels depending on demand. The best I have to calculate that is one of those clip on meters. Not sure if you'd consider that accurate but the amp figures I quoted above are from the manufactures data sheet so I presume they are reasonably accurate.

I presume I'd have to pay for the next MIC up? What work would need to be done inside the house to support it? Would the CU have to be changed?

Dardania · 15-11-2016 6:17am

+1 to tuco88 noting on measuring the actual draw to each appliance. And their advice generally

E.g. With the heat, the onboard display might say 6.6kw but does that account for conversion losses in the charger? So it might be a bit higher.

And for the heat pump data sheet, again the manufacturer might be noting a max demand worst care load there-the reality might be you can reduce that amount to something more reasonable. Don't some of those heat pumps have a resistive heater to boost water temperature or similar? The Laod quoted might include that. So measure the actual load - you have a split cool ammeter you are clamp on so you should be able to get a feel for it.

In practice your hair ighest load experienced will possibly be the heat pump starting up (in rush for a few secs) and the car pulling full current at the same time.
If you have a C curve MCB in the consumer unit, it should allow a bit of excess current for that start up until things settle down.

KCross · 15-11-2016 10:41am

Dardania wrote: »

+1 to tuco88 noting on measuring the actual draw to each appliance. And their advice generally

E.g. With the heat, the onboard display might say 6.6kw but does that account for conversion losses in the charger? So it might be a bit higher.

And for the heat pump data sheet, again the manufacturer might be noting a max demand worst care load there-the reality might be you can reduce that amount to something more reasonable. Don't some of those heat pumps have a resistive heater to boost water temperature or similar? The Laod quoted might include that. So measure the actual load - you have a split cool ammeter you are clamp on so you should be able to get a feel for it.

In practice your hair ighest load experienced will possibly be the heat pump starting up (in rush for a few secs) and the car pulling full current at the same time.
If you have a C curve MCB in the consumer unit, it should allow a bit of excess current for that start up until things settle down.

Im confident of the car charger figures. I've an app that connects to the car and it gives realtime power graphs. I've also cross checked the total power consumed over a charge as there is a kWh meter attached to the charger. The car is definitely drawing a constant 6.6kW's for several hours at a time.

The HP during normal operation draws 40A max on startup and settles to 22.5A when running. During the very cold weather it occassionally has to supplement its power by adding in resistive heating. It is capped at 4kW extra resistive heating and in that mode its max operating current is 40A. This is a rare occurrence but it can happen which is why I think I might have a problem come the winter as that resistive heating has not been used since I got the car. I can disable the extra 4kW easy enough but I'd rather not.

With the heat pump and the car charging together I am almost certainly in the 50A+ bracket and possibly more with resistive heating added in. I think I am cutting it fine. All it would take would be an oven or something to be turned on along with the base house load for lights/TV's etc and I could blow that 63A fuse.

Is there no such thing as a 70A consumer unit fuse? That extra few Amps would be enough.

What confuses me is the section of the ESB form (NC2) which says that 70A is max allowed for a 16kVA connection. In reality it seems that 63A is the max since thats whats in the consumer unit.
https://esbnetworks.ie/docs/default-source/publications/connection-to-a-single-domestic-dwelling-or-farm-premises-application-(nc2).pdf

Here is the section that describes the currents on that form

15-11-2016 12:36pm

I haven't wired a domestic installation in a very long time, however I am sure that the "standard" 12 kVA 2supply has a 63A switch fuse in the main distribution board backed by an 80A ESB fuse.

KCross · 15-11-2016 12:50pm

2011 wrote: »

I haven't wired a domestic installation in a very long time, however I am sure that the "standard" 12 kVA 2supply has a 63A switch fuse in the main distribution board backed by an 80A ESB fuse.

That isnt what the ESB engineer told me on the phone yesterday. He said 12kVA supply has a 60A fuse and 16kVA supply has an 80A fuse. What you are saying is also at odds with what @tuco88 said above about 50A in CU followed by 63A. Maybe they changed their practices?

Otherwise, whats the point of paying for the increased supply?

15-11-2016 1:50pm

KCross wrote: »

That isnt what the ESB engineer told me on the phone yesterday. He said 12kVA supply has a 60A fuse and 16kVA supply has an 80A fuse. What you are saying is also at odds with what @tuco88 said above about 50A in CU followed by 63A. Maybe they changed their practices?

Otherwise, whats the point of paying for the increased supply?

Like I said, it's been a while, I could be wrong

I work exclusively in the industrial sector (excuses, excuses.......)

17larsson · 15-11-2016 8:35pm

2011 is right. The standard ESB 12kVa supply is 80A fuse at the supply and 63A at the customers end

Dardania · 15-11-2016 9:18pm

Interesting wording on page 91 of this:
https://www.esbnetworks.ie/docs/default-source/publications/national-code-of-practice

...MCB of not less than 63A...

Maybe there's a higher rated MCB possible? I've seen adjustable , albeit lower current ones for precisely matching a motor overload - maybe you could get a 70A MCB?

Water John · 15-11-2016 9:21pm

One would wonder is this area being deliberately obfuscated.

Steve · 15-11-2016 9:53pm

What meter have you OP?

The max I've seen direct is 63A fed with 16sq, above that you need CT's.

15-11-2016 10:01pm

Steve wrote: »

What meter have you OP?

The max I've seen direct is 63A fed with 16sq, above that you need CT's.

According to the National Code of Practice for Customer Interface:

Single phase whole current meters will be used to measure loads up to 80A per phase. In general, three phase whole current meters will be used to measure loads over three phases up to 80A per phase. Current transformers with matching meters will be used to measure loads in excess of 80A per phase. Allowances for potential load growth should always be made.

Steve · 15-11-2016 10:08pm

2011 wrote: »

According to the National Code of Practice for Customer Interface:

Single phase whole current meters will be used to measure loads up to 80A per phase. In general, three phase whole current meters will be used to measure loads over three phases up to 80A per phase. Current transformers with matching meters will be used to measure loads in excess of 80A per phase. Allowances for potential load growth should always be made.

Same as yourself, I haven't done this in a while. Back in my panel building days ESB would not allow a fuse over 63A to a WC meter - domestic or commercial. 80A required a CT chamber with copper busbar links.

Maybe it's all changed now, don't know.

ED:

On reading that, ESP will accept a 80A BS88 fuse protecting the meter. However, they say a NZ type fuse should be on the board incomer.. do these go above 63A?

15-11-2016 11:02pm

Have a look at page 3 of this.
It states that a 12 kVA supply can have an average maximum demand of 52 A over 10 minutes. In my opinion a 50 A fuse is undersized for this as the fuse rating is less than the design current.
Whereas the 16 kVA supply can have an average maximum demand of 70 A over 10 minutes. In this case I feel that a 63 A fuse is undersized for this as the fuse rating is less than the design current.

KCross · 15-11-2016 11:54pm

17larsson wrote: »

2011 is right. The standard ESB 12kVa supply is 80A fuse at the supply and 63A at the customers end

If that's the case what fuses exist for the increased supply(16kVA)?

@Steve , I have a modern day/night ISKRA digital meter.

Tuco88 · 16-11-2016 2:13am

Whats the point in a 12 kva when it's fused the same as a 16 kva?

Did the ESB engineer not say this to you over the phone.

It's been a while for me too in the domestic seen ðŸ˜†

Tuco88 · 16-11-2016 2:27am

2011 wrote: »

Have a look at page 3 of this.
It states that a 12 kVA supply can have an average maximum demand of 52 A over 10 minutes. In my opinion a 50 A fuse is undersized for this as the fuse rating is less than the design current.

Whereas the 16 kVA supply can have an average maximum demand of 70 A over 10 minutes. In this case I feel that a 63 A fuse is undersized for this as the fuse rating is less than the design current.

If you have the 12kva mic, your maximum demand for ten minutes is 52 amps as stated. Personally I won't like to be pushing it with a 63amp fuse?

I have always seen the 16 kva as the standard now.

Is the issue here with fuse sizes or lack off?

KCross · 16-11-2016 10:53am

Tuco88 wrote: »

Whats the point in a 12 kva when it's fused the same as a 16 kva?

Did the ESB engineer not say this to you over the phone.

I agree. There must be some difference between the fuses between 12kVA and 16kVA otherwise paying for the increased supply is a scam.

I have the increased supply. The ESB engineer confirmed that I have an 80A fuse. That is a fact.

Tuco88 wrote: »

I have always seen the 16 kva as the standard now.

Its only the standard if you pay for it. The standard is still 12kVA unless you stump up the dosh. Do you mean the standard in that most people building a new house opt to pay for 16kVA? Why would they? Most dont need it.

Tuco88 wrote: »

Is the issue here with fuse sizes or lack off?

So, yes, to get back on topic. My original question has nothing as such to do with the differences between 12kVA and 16kVA.

The question is, the ESB new connection form(referenced earlier in this thread) says I can use 70A on a 16kVA supply and they have an 80A as their fuse for peaks/headroom above that.

My CU has a 63A fuse so Im not able to utilise all of the increased supply.

I want to utilise the 70A as I feel I am too close to the 63 right now. Is it possible(within regulation) to utilise the 70A and if so, how?

BoatMad · 16-11-2016 11:14am

What do the wiring rules say on the subject , I've mislaid my copy of the 4th edition

16-11-2016 12:04pm

BoatMad wrote: »

What do the wiring rules say on the subject , I've mislaid my copy of the 4th edition

It doesn't provide a fuse rating for this.
However ET101 does state that the protective device should have a higher rating than the design current and the design current for a 16 kVA supply could be up to 70 A (see above).

16-11-2016 12:14pm

However what ever main fuse is selected on the customer side it should be suitably rated to ensure that it will blow rather than the ESB fuse under overload conditions.

Dardania · 16-11-2016 12:31pm

2011 wrote: »

However what ever main fuse is selected on the customer side it should be suitably rated to ensure that it will blow rather than the ESB fuse under overload conditions.

Difficult to achieve discrimination for overload of 70A, with an upstream of 80A...

BoatMad · 16-11-2016 1:03pm

2011 wrote: »

However what ever main fuse is selected on the customer side it should be suitably rated to ensure that it will blow rather than the ESB fuse under overload conditions.

I think nobody disputes this , but I suspect a 63A fuse on a 16kva capable distribution is incorrectly specified , the OP is correct in his assumptions that the distribution fuse should increase with the rise in input power ASSUMING the distribution board is correctly speced and wired for the higher power

16-11-2016 1:57pm

Dardania wrote: »

Difficult to achieve discrimination for overload of 70A, with an upstream of 80A...

Agreed, if it is 80A.....

Someone from the ESB previously suggested it is a 100A fuse.
I can't find anything definitive though.

In my opinion it would've best for the REC to talk to the ESB to find out what size fuse is installed on their side and work back from there. I would be interested in measuring the load with the heat pump on and electric car charging.

I remember measuring the load for heat pump for alarms house and it was under 23A.

Water John · 16-11-2016 2:15pm

HPs would vary a lot on input/output. But most would be under 25A. that would be about 16Kw output. Please correct me, if I'm out a bit.

But looking to the future. A modern house could have HP + 2 EVs. That could be a base load during the night. What about the electric shower?
Are we into the area of priority access no matter what is supplied?

BoatMad · 16-11-2016 2:17pm

Water John wrote: »

HPs would vary a lot on input/output. But most would be under 25A. that would be about 16Kw output. Please correct me, if I'm out a bit.

But looking to the future. A modern house could have HP + 2 EVs. That could be a base load during the night. What about the electric shower?
Are we into the area of priority access no matter what is supplied?

No we are into having a grid that can meet the demands as heating and transport move to electric power

in the UK new build are now standard at 24KVA, in the US, 200-400A connections to houses are not uncommon

we need to move on from the " rural electrification " era !

Water John · 16-11-2016 2:21pm

I agree very much that we are or should be moving to a mainly electric environment. Do you think we have a plan? Like hell we have. No vision of the carbon neutral economy.

Distribution board has 63A fuse and ESB fuse is 80A. How do I utilise the extra 17A

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