Meter overload

[kyrre]

I have 30/100 single-phase feeding a 2 story house and a separate apartment.

When we have visitors and all showers are in use i get some peeks blowing my 100 A knife fuse on the intake cable.

​I will separate the intake cable so i have 2 different fuses feeding the house and the apartment. But then i will / may get some peeks going over the 100 A, as i recall in your post before you said the meter may keep up with a certain overload.

I may get a peek at 120 A when and if all is used at same time. Would that blow the meter or should it be within the safety margin in the meter..

I have 100 A main breaker in the house and 32 A in the apartment.

Thanks for any answer....

[Crossy]

If you are opening a 100A fuse you are WAY over 100A load (a 100A BS88 fuse will carry 200A for 3 minutes and 150A virtually forever). http://www1.cooperbussmann.com/pdf/deb5cfba-0923-4a7b-8827-cbda8a541498.pdf MCBs are much quicker (about 40 seconds for a similar overload) so you can get away with a larger value but I doubt that's going to help in this case.

Meters are very robust but I really wouldn't be fusing over 100A on a 30/100. Can you not time your usage so you don't apply the whole load at once (set the alarm clocks to different times)?

Get a cheap clamp-on ammeter and check the actual load under various conditions.

It may be possible to get the apartment on a separate meter of its own, or possibly a 3-phase 30/100 supply which would easily cope (put the apartment on one phase the house on another), talk to your local supply authority.

[kyrre]

I will bring the fluke amp meter next time to check the actual load.

I have the Chang 100A 600V knife breaker at the loft, so it is already hot...

When the fuse broke we had:

4 x 6kw heaters in use at same time after a day at beach.

+ some small appliances like computer and light. Waterpump.

So the actual use adds up to about 26kw. Slightly over the theoretical 22kw for a 100A fuse.

I will remove one heater to improve it and connect it to the next bathroom as it is on the other side of the wall for the kitchen.

Thanks for the answer.

[Crossy]

Yeah, it's all that water heating that's killing you (or at least your fuses), if you're running aircon as well no wonder the fuse is going to heaven.

A nice refreshing COLD shower after the heat of the beach perhaps?

Have you considered gas water heaters or a tank type electric heater (much lower peak load)?

[DerekMarshall]

why not get solar water heater? they are pretty effective even during the winter. You will save on your load currents and $$ on your bills.

Edit:

I dont know if you can get them here but I have seen calor/butane gas (i.e gas bottled) water heaters in Spain that instantly heat up water when needed

in the same way as say an electric shower (also seen gas equivalents of electric showers).

Also in Spain during the cold winters there are air con systems that are powered by calor/butane gas (i.e gas bottled) to heat homes. might help take load off current also.

Edited October 21, 2014 by DerekMarshall

[kyrre]

the problem in existing building is the pipes are not connected throughout to the different rooms..

I would say that normally this wont happen so often. Normally you have a more spread use pattern distributing the load.

This one instance was when we had a lot of visitors in the house + the extended Thai family.making a que at all bathrooms :-)

[IMHO]

the problem in existing building is the pipes are not connected throughout to the different rooms..

I would say that normally this wont happen so often. Normally you have a more spread use pattern distributing the load.

This one instance was when we had a lot of visitors in the house + the extended Thai family.making a que at all bathrooms :-)

In cases like this, just turn off the breakers for the water heaters in the rooms where the extended family are going to shower - overload problem solved

[Pib]

Electric metes are spec'ed to international standards like CEI/IEC 62053-11 Electromechanical Meters for Active Energy. The 100A max rating on a meter 30/100A meter is its max "continuous" operating capability, but they are supposed to be designed to handle a very significant short term overcurrent of at least 50% of max rated current. But this max overcurrent rating is based on a test of 1 millisecond overcurrrent; not minutes which a shower would take....and if it was some of my in-laws I think they can stand under a shower for hours. I expect a person will need to get detailed specs from each meter manufacturer as to the impact on their meter in an overcurrent status for minutes, hours, etc....I expect they would just say don't overcurrent it....plus that is proprietary data...go away.

Anyway, you can take a look a below Para 7.2 from above mentioned document talking Influence of Short Term Overcurrent.

[Crossy]

Pib, that spec. is for 1ms impulse overloads of 50 x I_max (so 5000A for a 30/100), the idea being that the meter won't get killed before the protective device opens in the event of a dead short.

I agree with your surmission that a 50% continuous overload is the most that would be acceptable which is in line with fusing using a 100A BS88 fuse or something like 120A C-curve MCB.

[Pib]

Here's a link to Mitsubishi Thailand Electric showing one of their 30/100A electric meters...for over-current they spec it at 120A (continuous for 30 minutes).

[Crossy]

I think we have definitively demonstrated that our OP should not fit a bigger fuse

[kyrre]

I not gone up the fuse size... but just have to find a way to deal with it..

Maybe split it by 32A and 64A so i don't blow all at same time.

And by reducing the heaters it should normally fall within good margins.

Thanks for all the good answers and clarifications...

[lopburi3]

You mention both knife switch and breaker so not sure which you have but seem to recall that before we replaced the fuse/knife switch several decades ago that there were different types of fuse material and some were instant blow and some slower so perhaps change of that would help? But believe breakers are now normal for main input lines everywhere. But change to breaker is not something I would do myself as want a dead line when working on electric - needs to be disconnected at meter first.

[kyrre]

well i have both. Because it is done in a non proper way when they built the apartment i have put i knife switch at the loft as the apartment was feed right of the main cables up there, but i want to replace them by putting a new set of cable outside with proper connections and separate main breakers.

[kyrre]

I need some help choosing my meter upgrade...Maybe i don't understand the PEA naming scheme for the different meters.

I have a 30(100) 1 phase meter today with 100 A breaker witch is to low for the house and one apartment sometimes.

They recommended i upgrade to no 18 on the list witch is a upgrade from 30 A 1 Phase to 30 A 3 Phase.

What i understand from the recommendation here i should go for a 15(45) 3 phase.

I have attached the list from PEA.

Is no 17 on the list the meter they call for 15(45) meter upgrade from 1 phase to 3 phase?

Is no 18 on the list a the meter they call for 30(100) meter upgrade from 1 phase to 3 phase?

I don't need a 3 x 100 A 3 phase as 3 x 45 A would be enough, and the upgrade price i also a lot in difference.

Is my presumption correct or way out!!!

[Crossy]

First off, did you manage to measure your actual maximum load?

The easy solution would be the 3-phase 30/100 and transfer the apartment load to a second phase leaving 1 phase unused (for that big workshop you're planning perhaps ).

BUT

There does seem to be a significant cost difference to the 3-phase 15/45.

The 15/45 will give you about 50% more oomph than you have now and would likely be sufficient (but you must check the loadings) but would require some juggling of the house wiring which may or may not be easy (you need to split the load between two or three phases.

The 30/100 would be three times the power you have now.

Any plans for more apartments etc on the same supply?

[kyrre]

I don't have any plans for more apartments..

I have nor measured any load yet, as i am gone bring the Amp meter with me back when i go home for a few weeks.

The 15/45 seems a lot cheaper yes, and it may be enough.

The wiring is not that much problem as i use a new consumer unit for 3 phase on 2. floor and use the old cable to supply the 1 phase in 1. floor.

To the apartment i gone get new cable anyway.

And the 3 phase i can connect to 3 air-con and water heater in 2. floor.

But i gone measure the load on each unit first and add them up before i decide for a 15/45 or 30/100

Crossy: Is the no 18 on the list actually a 30/100 3P Meter... As PEA say its 30A?

[Crossy]

Crossy: Is the no 18 on the list actually a 30/100 3P Meter... As PEA say its 30A?

Yes, that's the 30/100, it's purely terminology when they call it '30A', that's the nominal current, 100A is the continuous maximum.

[kyrre]

Thanks for the help all....

I have been thinking of the 2 options i have. The 15/45 meter would be to small to support my main consumer unit and would create a need for rewiring a lot.

So i will go for the 30/100 meter. This would provide enough on a single phase to each CU and one spare.

Today i have Schneider square D consumer units. What i have seen so far for 3 phase they are rater big for my needs as it would only be distributing the 3 phases to 2 different consumer units.

My need is a CU with 3 phase main breaker (or 100ma RCBO) with

1. 100A main breaker supplying the old consumer unit with 63A RCBO.

1. 63A/50A supplying the apartment consumer unit with 45A RCBO

And

2 or 3 16A/32 RCB/RCBO on the 3. phase supplying the air-con and heaters in 2. floor to offload the old consumer unit max load.

Any suggestion on solution here.

Does Schneider have smaller 3 phase units 9 slots needed?

OR is din rail type unit the best option.

Thankful for all answers.

[Crossy]

Personally I'd go DIN rail, Haco make 3-phase bus-bars but you'll need to go to a specialist outlet http://www.hacothailand.com/product-engshow.php?Page=13&setype=3&setype2=&txtsearch=

If you go with a 4-pole incomer (breaks the neutral) it is essential that you use one with a late-opening/early-closing neutral contact to prevent real nasties occurring when it operates (and of course ensure the neutral is connected via that contact).

If the supply is MEN it is not essential to open the neutral at the incomer, but many people like to do it anyway. The MEN link needs to be before any RCDs or you'll struggle to keep them closed.

[kyrre]

Thanks for answering Crossy.

If you go with a 4-pole incomer (breaks the neutral) it is essential that you use one with a late-opening/early-closing neutral contact to prevent real nasties occurring when it operates (and of course ensure the neutral is connected via that contact).

Do you have any spec, model or brand name for this unit?
Same as Haco R7-4100-30?

Used with a 3 Phase 4 Wire Insulated Busbar

And 2 pole circuit (H7-63-2C) breakers breaking neutral and live to each of the old consumer unit with main RCBO there.

[Crossy]

The R7-4100-30 is a 30mA RCD which you probably don't want on your main incoming supply.

Haco don't appear to do 3 or 4 pole MCBs over 63A so we need to look further afield.

ABB have a number of suitable devices http://docs-europe.electrocomponents.com/webdocs/0e27/0900766b80e279ef.pdf#page=34&zoom=auto,-163,842 but you'll need to talk to your local outlet to find what's available here

100A MCBs are not a cheap item, a 4 pole isolator would be a more cost-effective solution that does not compromise safety http://www.amazon.co.uk/HAGER-SWITCH-DISCONNECTOR-SB499F-552985/dp/B006L44UFU or http://www.ebay.co.uk/itm/HAGER-100A-SB499F-4-POLE-MCB-MAIN-SWITCH-DISCONNECTOR-AC22A-400V-/131335014958?pt=UK_BOI_CircuitBreakers_RL&hash=item1e942d4a2e

Use 3 x 100A BS88 fuses as protection for your meter.

[kyrre]

OK, Thanks again for the answer.

I think i have a look at the local shop in Naklua witch seems to have the most. If not i have a friend of the family who is electrical engineer working for the big condos in Jomtien.

Would the BS88 fuse fit into the Chang knife fuse holder(Flat lead/ink fuse) used in Thailand, or is it other holders for this.

[Crossy]

BS88 covers a wide range of fuse formats (Google it for pictures).

It is of course important that you have a ready supply of fuses just in case, so talk to your local electrical emporium.

Ensure that the fuses and holders you get are HRC (high rupture capacity), BS88 specifies 80kA but anything over 40kA should be fine in Thailand.

[kyrre]

Thanks again for the clarification.

So the path will then be:

30/100 Meter - BS88 Fuse - (Main Breaker - Sub breaker to each Consumer unit) - 2 Consumer units with RCBO.

And one spare(Or supply 2. floor Air con and heater)

I will take it up with the local supply store and see what he have in stock.

[Crossy]

Good idea to see what's available.

It may be wise to use a 3-pole 'Chang' knife switch as a fuse holder, you can pull the power to the fuses then, but I'd still have a proper 4-pole isolator in the CU which opens the neutral.

[kyrre]

I will try to get the proper 4-pole isolator as 1.st priority

If not the knife switch as second option.

If the supply store don't have it, i will ask a friend of the family witch is electrical engineer who has been working on the Viewtallay condos. The supply store we use is after his recommendations.

Thanks.