Voltage drop in house - what to expect

KCross wrote: »

I have the upgraded 16kVA supply.
I have a heat pump and an electric car (6.6kW). I also run various appliances at night (dishwasher and dryer mainly).

If you look at 525 in the National Rules for Electrical Installations you will see the following:

525.1 Under normal serviceable conditions, the voltage at the terminals of any current-using equipment shall be not less than the lower limit set by the manufacturer.


Based on this:
1) Do you know what the lower limit set by your manufacturer is for your heat pump?
2) Have you taken this measurement under load conditions when other large loads are also on? - If so what voltage did you measure?

525.2 The cross-sectional area of every current-carrying conductor shall be such that the drop in the voltage between the main supply point in the installation is not more than the following when the conductors are carrying the full load current:

- 4% of nominal voltage in installations and parts of larger installations rated not greater than 80A, circuits at extra low voltage excepted.

According tot eh above:
As the nominal voltage is 230 VAC this means that the maximum permissible volt drop is 9.2 VAC (**** 4% of 230).

**** Note: The ETCI have issued a few corrections / clarifications over the years so this 4% value may have changed. Perhaps other posters can advise. I am a little out of touch as I have been working on projects outside of Ireland for the last few years.

I have a UPS which shows voltage and I also have one of those cheaper plugin type energy monitors and it shows voltage as well.... its generally steady enough at 230V but I have seen it go as low as 216V when multiple items are running (particularly heat pump and car).

Hardly a calibrated test instrument, but perhaps it is an accurate reading.

Every item I turn on drops it another few volts.

This is because volt drop is a function of two things:
1) Resistance
2) Current.

So if you increase the resistance of any conductor within the circuit or increase the current flowing (by connecting more loads) thee volt drop will increase.

1)
What is the boards wisdom on this. Do you have to regularly drop below 207V for the ESB to do anything or is it enough to have it happen once or twice to "force" them to do something about it?

You did the right thing by contacting the ESB. They will assess with proper test equipment over a protracted period.

2)
If they do agree I have a voltage issue, what is the actual solution? Is it a new transformer? FYI: It is a shared transformer with about 4 other houses.

It could be. This will be decided on a case by case basis.

3)
If its a new transformer what size one should I be "insisting" on. I know I can't insist on anything as such but I'd still like to know so I can push things.

Leave that to the ESB. You can help them size it by providing them with an accurate description of your load profile.

I'm reasonably confident the cable sizes etc are good particularly for the heat pump and car charge point as they have dedicated cables and are sized according to spec. (e.g. charge point has 10mm2 cable).

Just because the cables are 10 mm sq. does not mean that they are correctly sized. For all you know the volt drop on the cable between the ESB meter and your distribution board is undersized. Therefore the volt drop is too high before it even reaches the 10 mm sq. Remember one of the factors that should influence cable size is the length of cable run.

Please answer the following:
How long is your 10 mm sq. circuit to the heat pump?
How many kW is the heat pump?
How long is the cable run from the ESB meter to your distribution board? I would think that this cable should be a minimum of a 25 mm sq.

KCross wrote: »

2) As you have said, I don't have industry grade measurement tools and I don't have a profile of the figures over time... just snapshots in time. I've seen it go to 216V with car, heat pump and general background house load.

If a correct reading this is not good.

True. UPS's tend to be fairly accurate though.

You can't make a blanket statement like that.
Some are, some aren't. You get what you pay for.

They are protecting equipment from low/high voltage so its not ****e electronics they are selling.

In every case? I don't agree.
For example, look at this beauty, it costs less than £40, somehow I doubt it is high quality.

The figure given by the UPS for voltage is the same the voltage figure I get from the plugin monitor so I'm inclined to believe the figures its giving me.

It is not my intention to say that you necesserialy have inaccurate measurements, I am just pointing out that perhaps they are inaccurate.

I am a heavy electric user and thats why I paid extra for the 16kVA connection so I'm hoping they resolve it if it is on their side.

Right now you can't be sure that the issue is not on your side. It is also possible that there is an issue on both sides.

I'm confident of the tails from the meter to my board is correct. It was sized on the basis of a 16kVA connection when the house was built. I paid extra for the tails once the electrician realised I was getting a 16kVA connection.

It would be interesting to know the following with all measurements taken at the same instant:
1) What the voltage is at the meter box at a time of heavy (but normal) load use.
2) What the voltage is at distribution board at a time of heavy (but normal) load use.
3) What the voltage is at the heat pump at a time of heavy (but normal) load use when the heat pump is running.

Im also confident of the charge point cable, if anything that's over sized.

Perhaps it is, but it dose not necessarily follow that the heat pump is.

I haven't eyeballed the heat pump cable. I'll double check that one. The heat pump was installed by a reputable company and the wiring was done by my own electrician under their instruction and they cross checked so they had no reason not to pull up my electrician on it if he under sized it. It would in their best interest to call him out so I'm assuming its good but I will double check.

Also check length of run.

About 20m, at a reasonable guess, from the distribution board to the meter.

That is a long cable run!
So if we look at this table we can see that the volt drop per amp per meter for a 16 mm sq. T & E cable is 0.0028 volts.

So let's say you are drawing65 A and your distribution board is fed with a 16 mm sq. T & E cable (a pretty standard cable for supplying distribution boards) then:
The volt drop on a 16 mm sq. cable is = 65 x 20 x 0.0028 = 3.64 V
So this means that the volt drop from the distribution board to the heat pump should not exceed 5.56 volts (max. permissible VD of 9.20 - 3.64 volts)

The HP is rated 12kW output. (NIBE F1145 12kW)

So what size electrical load is it? If the output is 12 kW the electrical input will be considerably less.

KCross wrote: »

1) A "constant" 230V ±3%.... so more like 223-237V

I doubt that you would get something that steady. If you were part of a housing estate that is fed from a large transformer then your supply voltage would be more stable.

2) They will deliver more than 230V so that when it drops its more acceptable to my equipment? i.e. I will still see the same voltage drops as the HP and car loads come on.

As larger loads are switched on a larger volt drop can be expected. This is particularly the case when a motor starts such as the compressor in the heat pump. This problem is exacerbated if the installation is fed from a smaller transformer (on the ESB side).

FYI: Right now, when the heat pump starts the voltage drops by 4V according to the two monitors I have. Assuming my internal wiring is good is that normal or not?

Its not really that surprising.
The starting current for a direct on line motor can be 6 to 8 times the full load current. So when the compressor motor starts the current demand soars for a short time. The volt drop increases as the current increases and then drops off again as the motor current decreases.

KCross wrote: »

I understand the starting currents are much higher but I notice that the voltage stays 4V down while the heat pump is running.

Would you expect that?

Let’s put it this way:
All conductors have a resistance. Let’s say we have a conductor with a resistance of 5 ohms. If we pass a current of 10 amps through it the volt drop across it will be 5 x 10 = 50 volts.
Next, consider all of the conductor resistances to be fixed (because they pretty much are). This means that any increase in load (therefore current) will result in an increased volt drop. Some of the volt drop you are experiencing will be as a result of cables on the ESB side.

As another data point, the voltage was showing as 223V this morning (8:30am) with no heat pump (or anything of note actually) running at the time!

This tells you that there is a bigger picture. Perhaps for example, others connected to the same transformer are drawing a larger load than normal at this time, hence my question in my last post. Can you could answer this question?

KCross wrote: »

Are you referring to these questions...

No, they were from an earlier post. My bad, I did not ask the question I intended to, which is:

Are you in a rural area, or are you sharing a transformer with very few others?

Another point to consider, what load profile did your electrical contractor portray to the ESB when applying? My concern is that you may be using more power that was applied for. In addition when you increase the load in the future you may go further beyond the supply capacity originally applied for. The consequence of this is you may be charged for the costs associated with rectifying this issue.