Din mounted KWH meters.

[Mrdjc]

Hi,

I'm looking for a DIN mounted KWH meter to go inside a consumer unit, to measure how many KWH's get used.

I've found single pole width meters in both analogue and digital form, but they only go up to 32A.

If I had an incomer of 63A and a total maximum load exceeding the 32A rating of the meter, I obviously would require something larger.

I have found a 100A meter, but its 4 pole width.

Looking for something as compact as possible, but with a high enough rating so it can withstand more than 32A through it.

Can someone point me in the right direction?

Thanks in advance.

 

[Mrdjc]

Just found this:
http://www.neweysonline.co.uk/schne...230v-ac/1051008966/ProductInformation.raction

£247,- with VAT.... that's enough electricity to last a year out here!

Also found this:
http://www.smartpowershop.co.uk/socomec-countis-e12-mid-certified-meter.html

£150,-

Considering the single pole 32A ones are around £30,- there must be some middle ground somewhere surely?!

 

[Mike2007]

Why don't you use a standard single phase meter instead, mounted to one side of CU? Cost peanuts to buy.

 

[Mrdjc]

Aesthetics mainly!
The CU will be recessed into the wall, so you barely notice it.

Adding another meter alongside would require a surface mount or recessing another box, then the extra cables would require covering over etc, it will look out of place and a right mess.

The space the CU is going is rather limited, hence I want to stick it all in one box, rather have a few spare module spaces than having an ugly meter hanging on the side with cables tailing off it.

I've found a ABB one that is also supplied in Slovakia going for around £100,- It's double width, and up to 65A.

http://www.shmmetershop.co.uk/ABB-O...nnection-MID-Approved-meter-to-Annex-B-D.html

Think that's what I'll end up getting.. unless someone else comes up with a ingenious idea.

 

[bhm1712]

http://www.smartpowershop.co.uk/ele...ct-connection-with-pulse-output-48503000.html

£98

 

[Mrdjc]

Thanks for replying
Yes I found that one too, but its 3 module width.

So looks like its a toss-up between the ABB and the Countis for around £100,-

 

[JohnW2]

So looks like its a toss-up between the ABB and the Countis for around £100,-

I don't suppose 45A would be enough for you, would it? (no price quoted):
http://www.pjwmeters.co.uk/product_detail.php?id=28

Kind Regards, John.[/url]

 

[Mrdjc]

The thing is.

100A fuses from supply to meter. (outside)

10mm2 incomer for house, 3 phase.

63A MCB on each phase Into first box.
1st Phase - House side A -> 63A 10mm
2nd Phase - House side B -> 63A 10mm
3rd Phase - Garage/Workshop -> 63A 10mm
3Phases - 3phase socket -> 32A 4mm

House side A has
6A - Lights
16A - Bedroom
16A - Bathroom/Utility
16A - Storage Room
16A - Kitchen/Dining room
20A - Kitchen worktop

If all circuits were maxxed out it would be close to 90A. The supply is limited to 63A.

Realistically it is never going to max out, but its hard to say what the maximum draw at one time would be.

45A @ 230V is 10.3KW.

If someone had a vacuum cleaner, hair-drier, deep fat fryer, electric kettle and Microwave on at the same time, it would be exceeded.

Hence trying to find a meter which will withstand the maximum permissible current in the CU before the MCB trips out.

I noticed most CU's come with 100A master switches, but since our incomer is only 10mm2 its already down to 63A.

Since the wiring is up to 63A according to the tables, it makes sense to end up with a large enough protection so it doesn't trip as a nuisance, just in case there is a large demand.

 

[JohnW2]

...If all circuits were maxxed out it would be close to 90A. The supply is limited to 63A. Realistically it is never going to max out, but its hard to say what the maximum draw at one time would be. 45A @ 230V is 10.3KW. If someone had a vacuum cleaner, hair-drier, deep fat fryer, electric kettle and Microwave on at the same time, it would be exceeded. Hence trying to find a meter which will withstand the maximum permissible current in the CU before the MCB trips out.

It may be worth looking in detail at the specs of these meters, particularly the 45A one. It could be that it can 'withstand' a lot more than 45A, even though the accuracy of measurement would not be guaranteed (or might not be accurate) above 45A. Old-fashioned UK domestic electricity meters very often had "45A max" written on them. However, they could (and often did!) easily 'withstand' 80A or more, but they weren't certified as accurate beyond 45A.

Kind Regards, John.

 

[JohnW2]

Hence trying to find a meter which will withstand the maximum permissible current in the CU before the MCB trips out.

I should perhaps have added that, of course, a B63 MCB will carry a current of about 91A (1.45*In) for around an hour before tripping.

Kind Regards, John.

 

[Mrdjc]

Thanks John, that is very informative.

I don't think accuracy is that much of an issue as the times it will exceed 45A won't be that great.

It is just to give Granny a ball-park figure of what she is consuming in the whole house.

I never knew that an MCB would carry a greater current, I know there are different types of MCB, but thought that this would already be included in their maximum rating!

Is there any good documentation I can read up on this? For example where did you find 1.45?

Regards,
Daniel.

 

[JohnW2]

Thanks John, that is very informative. I don't think accuracy is that much of an issue as the times it will exceed 45A won't be that great. It is just to give Granny a ball-park figure of what she is consuming in the whole house.

In that case, as I suggested, you need to find out the 'maximum withstand' currents of the meters you're looking at - since they could well be appreciably higher than the 'rated' (for accurate measurent) currents.

I never knew that an MCB would carry a greater current, I know there are different types of MCB, but thought that this would already be included in their maximum rating!

A common misconception. A Type B MCB will never trip at 1.1*In, and the characteristics are such that they will trip in about an hour at 1.45*In. The higher the current, the sooner will it trip ....

Is there any good documentation I can read up on this? For example where did you find 1.45?

For starters, look at this and this one.

Kind Regards, John.

 

[Mrdjc]

Thank you for those links John.

One thing that confuses me though, and having read through various posts on here.

The cables Rating should be greater or equal to the MCB's rating?

Iz >=In

Running 1.45 x In for up to an hour before tripping is perfectly permissible?

Say I were to take 3x2.5 from this datasheet:
http://www.prakab.cz/fileadmin/cont...kabely/Instalacni_ploche_kabely/cykylo_en.pdf

Which would give me a CCC (Iz) of 25A.

I installed a 16A MCB type B (In)

I2 = 1.45 X In = 1.45 x 16 = 23.2A for up to 1 hour.

In this case it would be fine because Iz is > I2

But say I used a 3x1.5 from the same datasheet above, 18A Iz

I installed a 16A MCB Type B (In)

I2 = 1.45 X In = 1.45 x 16 = 23.2A for up to 1 hour.

I am now exceeding the Iz by 5.2A for up to 1 hour.
Is this permissible?

How exactly is Iz calculated/computed?
Is it the end all and be all or can you subject it to 1.45 x Iz for up to 1 hour?

Do you need to reverse compute the Iz for each cable depending on the In x 1.45 to see if the Iz is adequate?

Or can I simply say In <= Iz and that's enough?

Not I2 <= Iz ?

Where exactly does CCC lie in relation to all of this?

Is Iz a "safe" figure given by manufacturers which can be exceeded for a short time, or is it the critical figure which when exceeded, even momentarily, can cause damage?

 

[JohnW2]

Thank you for those links John. One thing that confuses me though, and having read through various posts on here. The cables Rating should be greater or equal to the MCB's rating?
Iz >=In
Running 1.45 x In for up to an hour before tripping is perfectly permissible?

Yes, that also had me totally confused, and it was a need for clarification of this that was one of the reasons which initially brought me to the forum.

The apparent explanation (which is, indeed, consistent with everything else) is that the tabulated values of 'maximum permissible current carrying capacity' (i.e. Iz) are not quite what they seem, but actually take into account the fact that current may exceed these figures by a factor of 1.45 for up to one hour. In other words the tables are designed so that (tabulated) Iz >=In is OK.

Note that the 1.45 figure (and hence the tabulated Iz figures) apply specifically to Type B MCBs. If one has some other sort of overcurrent protection device (e.g. a fuse), then one does have to adjust one's calculations to take into account the different (from 1.45*In) current that may flow for up to one hour.

Kind Regards, John.

 

[Mrdjc]

Thank you very much for clarifying that

So, if I understand this correctly:

Iz takes into account that its own value may be exceeded up to 1.45 times for up to an hour.

If I take an alternative device (Type C or Fusible wire or something), I may take my 1.45 times Iz value, deduct the Iz value from that.

Compare it to the new rating given by the alternative fuse, and with that information, decide on the In rating or alternative Iz rating if it varies too greatly from Ib.

So in theory:

Iz from datasheet is 24A.

1.45 X 24A = 34.8A

34.8A - 24A = 10.8A extra permitted for up to an hour.

So I can say (Coefficient of fuse) x In <= Iz x 1.45

?