House Renovation and Maximum Import Capacity

John T Carroll

A relation of mine is renovating a house in the city which has a existing supply which I presume has a MIC of 12 Kva (52A) as the existing switch fuse is 63A.
The house will be rewired and she understands that a NC2 form must be filled in and submitted. I did a few calculations for her based on a 9 Kw shower, a 14.5 Kw cooker, a washing machine, a dish washer, and a cylinder (elect) immersion heater. I was a bit shocked with the MIC number that I came up with even allowing for the cooker diversity factor. The MIC that I calculated is 114A, made up of the following in Amps, Shower:39.0,Cooker:26.0, Wash Machine 10.9, Dish washer:10.9, Immersion:13.0, Electric Kettle:8.7. Lighting:5. Now I know that hundreds of houses have that kind of installation and never blow the 63A fuse as all those appliances arn't on together but my queries are, is there any other diversity factor applied when submitting these figures, if not then will/would the ESB consider installing a power supply to meet these theoretical figures. Alternatively, if she wanted to meet the 12 Kva (52A) existing limitation, would she have to delete a number of appliances to meet it?. I suppose she could ask for the existing 12 Kva be upgraded to the other standard 16 Kva (70A) and make the sum of her appliances fit this.

Joe1919

Fuses often come with a specification called the fuse time current characteristic curve. For example, one manufacturer of HRC fuses specify that their 63 amp fuse can carry up to 100 amps for 2000 seconds. So its probably the case that the ESB fuse with withstand a few extra amps for the period while someone is taking a shower.
However, there is a thing called fuse fatigue in some types of fuses and this is a sort of thermal metal fatigue that can happen when the fuse becomes very hot due to exceeding its rated capacity over a period of time.

However, I would be interested in knowing the make/manufacturer/type in the case of ESB main fuses and checking specification (fuse time current characteristic curve) for same.

Risteard81

One word: diversity.

John T Carroll

Risteard81 wrote: »

One word: diversity.

I have applied a diversity factor calculation of 10+(63-10)*30% for the 14.5 Kw cooker which gives 26A, don't know if the ESB use their own factors for any other appliances when this form is filled in but my cousin would obviously like to be able to use the available 12.0 Kva (or maybe 16 Kva) capacity, is this likely with her proposed appliances?.

Joe1919

There are fairly typical situations where the 63 amp is exceeded. One case I know, for example is a couple who have inherited a house that they visit only on weekends. So during the winter, the arrive at the house that is stone cold from being vacant. They arrive and the first thing they do is turn on a 1.8kw oil radiator and 2kw fan heater in living room. One of the couple goes into bathroom and turns on downflow 2 kw fan heater and 2kw immersion heater and gets ready to take a shower after the long journey. She also turns on bedroom heater 2kw so things are nice and cosy while she dresses. Meanwhile, the other person turns on electric cooker for making a meal (1 ring and grill/oven = 3.5kw). So while the 9kw shower is being used, they are consuming over 22 kw which is close to 100 amps.
The couple have never blown the main fuse. They have however tripped the 20A mcb on the plug circuits and these had to increased and some heaters had to be pluged into alternative circuits (different socket)
Incidently, the house has a solid fuel heating appliance but this is very often not used and they are very dependent on electrical heat in winter.
I dont think the above situation is unusual.

Risteard81

John T Carroll wrote: »

I have applied a diversity factor calculation of 10+(63-10)*30% for the 14.5 Kw cooker which gives 26A, don't know if the ESB use their own factors for any other appliances when this form is filled in but my cousin would obviously like to be able to use the available 12.0 Kva (or maybe 16 Kva) capacity, is this likely with her proposed appliances?.

You need to consider diversity for the installation as a whole. Not only will circuits possibly have diversity factors, but also the installation.

Are you liable to be in the shower whilst all cooker elements are on (and haven't started cycling on and off), with all socket circuits fully loaded and all lights on, etc.? Of course not.

And also any high loading will be for a relatively short period so that it can nearly be discounted as the cables won't have heated up nor will protective devices have operated.

John T Carroll

Risteard81 wrote: »

You need to consider diversity for the installation as a whole. Not only will circuits possibly have diversity factors, but also the installation.

Are you liable to be in the shower whilst all cooker elements are on (and haven't started cycling on and off), with all socket circuits fully loaded and all lights on, etc.? Of course not.

And also any high loading will be for a relatively short period so that it can nearly be discounted as the cables won't have heated up nor will protective devices have operated.

I understand that from a practical point of view as my own house has all the proposed appliances and the 63A fuse has never blown in over 44 years so when the NC2 form is submitted can (my cousin) just request a MIC of 12Kva knowing that the "real" diversity factor will mean that the 52A limit is rarely exceeded?.

Risteard81

John T Carroll wrote: »

I understand that from a practical point of view as my own house has all the proposed appliances and the 63A fuse has never blown in over 44 years so when the NC2 form is submitted can (my cousin) just request a MIC of 12Kva knowing that the "real" diversity factor will mean that the 52A limit is rarely exceeded?.

I wouldn't even say that it will be rarely exceeded. It almost certainly won't ever be exceeded. The DSO might allow for about 2-3kW consumption per house. That is the reality of diversity.

John T Carroll

Risteard81 wrote: »

I wouldn't even say that it will be rarely exceeded. It almost certainly won't ever be exceeded. The DSO might allow for about 2-3kW consumption per house. That is the reality of diversity.

The NC2 form states that with a MIC of 12 Kva (52A) that the maximum allowable switched load is 9 kva and that a maximum storage heater capacity
of 9 Kw is allowed so I think this bears out what you are stating.

Maybe MIC should be changed to MDIC, Maximum Diversified Import Capacity?

2011

A few points:

First off with the exception of the 14.5kW cooker your relation's electrical loads are not "abnormal". Unless your relation is cooking for an unusually high number of people the cooker will use as much electricity as a smaller unit. Typically both ovens and all four / five rings are not on at the same time with all thermostats reading below the set point while someone is in the shower.

Have a look at the fusing caricteristic and you will see how fuses are designed to cope with short duration over currents.

Ways to reduce the load:

1) I would recommend that they avoid using the immersion even if there were no MIC concerns.

2) 5A of lighting is extremely high (>1.1 kW). Change to energy efficient lighting.

3) Install an Owl energy meter and monitor the electrical load. Worst case scenario I would ditch the instantaneous shower or replace the cooker with a "normal" sized or gas cooker before increasing MIC.


From esb.ie website:

You must choose the capacity that meets your needs. (From our experience this is always much lower than the sum of the kilowatt ratings of all the equipment that you plan to install).

I am sure that your own house has similar loads. Perhaps install an Owl energy meter in your own home and observe it. I think that you will be pleasantly surprised by how little power you actually consume.

John T Carroll

2011 wrote: »

A few points:

First off with the exception of the 14.5kW cooker your relation's electrical loads are not "abnormal". Unless your relation is cooking for an unusually high number of people the cooker will use as much electricity as a smaller unit. Typically both ovens and all four / five rings are not on at the same time with all thermostats reading below the set point while someone is in the shower.

Have a look at the fusing caricteristic and you will see how fuses are designed to cope with short duration over currents.

Ways to reduce the load:

1) I would recommend that they avoid using the immersion even if there were no MIC concerns.

2) 5A of lighting is extremely high (>1.1 kW). Change to energy efficient lighting.

3) Install an Owl energy meter and monitor the electrical load. Worst case scenario I would install ditch the instantaneous shower or replace the cooker with a "normal" sized or gas cooker before increasing MIC.


From esb.ie website:



I am sure that your own house has similar loads. Perhaps install an Owl energy meter in your own home and observe it. I think that you will be pleasantly surprised by how little power you actually consume.

Thanks 2011, the ESB quote below is the one that I was looking for as I was a bit hung up on the "official" NC2 form as I thought that maybe it had to include the sum of all the equipment Kw rating, I'm very happy now. John

"You must choose the capacity that meets your needs. (From our experience this is always much lower than the sum of the kilowatt ratings of all the equipment that you plan to install)."

Dardania

Risteard81 wrote: »

I wouldn't even say that it will be rarely exceeded. It almost certainly won't ever be exceeded. The DSO might allow for about 2-3kW consumption per house. That is the reality of diversity.

ESBN used advise me back in my consulting engineering days that I should allow 2.5kVA for a 2 bed, and add on 0.5kVA per additional bedroom, in an apartment complex - this was to size the main distribution for a development, so different story to OP.

Risteard81

Dardania wrote: »

ESBN used advise me back in my consulting engineering days that I should allow 2.5kVA for a 2 bed, and add on 0.5kVA per additional bedroom, in an apartment complex - this was to size the main distribution for a development, so different story to OP.

I know it's different to his maximum demand including diversity, but my point was that the reality of diversity is that we can get by on very little load in reality.

John T Carroll

Joe1919 wrote: »

There are fairly typical situations where the 63 amp is exceeded. One case I know, for example is a couple who have inherited a house that they visit only on weekends. So during the winter, the arrive at the house that is stone cold from being vacant. They arrive and the first thing they do is turn on a 1.8kw oil radiator and 2kw fan heater in living room. One of the couple goes into bathroom and turns on downflow 2 kw fan heater and 2kw immersion heater and gets ready to take a shower after the long journey. She also turns on bedroom heater 2kw so things are nice and cosy while she dresses. Meanwhile, the other person turns on electric cooker for making a meal (1 ring and grill/oven = 3.5kw). So while the 9kw shower is being used, they are consuming over 22 kw which is close to 100 amps.
The couple have never blown the main fuse. They have however tripped the 20A mcb on the plug circuits and these had to increased and some heaters had to be pluged into alternative circuits (different socket)
Incidently, the house has a solid fuel heating appliance but this is very often not used and they are very dependent on electrical heat in winter.
I dont think the above situation is unusual.

Just came across a few numbers from Dec 25th 2014 in my own house, I had 2X2.5 Kw and 1X1.5 Kw oil filled rads in operation as my heating had sprung a underfloor leak and with eight people in the house on Christmas morning there was a big demand. I dont have an owl energy monitor but I monitored the meter disc doing 20 revolutions in 18.4 secs which with 225 revs/kwh gave a load of 17.4 Kw or nearly 76 Amps, but one of the the main culprits in this was a 9.0 Kw shower which was in use at that particular time. My normal electrical usage is 12.5 to 13.0 Kwh/day but there can be a big difference between a max demand and a average.

whizbang

If you lived in Rome, your standard MIC is 3Kw. The trip point is about 5% overload.

You have to switch off the washing machine to put the kettle on.