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Posted By Topic: Property exceeding maximum demand

Phil1605
Mar 11 2020 18:27

I am working on an installation where they have added a second dwelling so it now has 2 kitchens, 2 hot water cylinders, air con and spa pools. I think this puts this well over 63amps but they do not want another phase installed as I have requested. If both dwellings are connected and exceeding 63a is this work deemed to be non compliant?? I have read about limitation and believe I could put fuses in the meter box limiting each dwelling, which I will do but believe this will cause problems. Anyone have any suggestions or found themselves in a similar situation.
   

gregmcc
Mar 11 2020 19:51

From what you are saying I would say this is in the "Electrically Unsafe" area. I would advise the customer in writing along with possible problems that would likely arise such as damage to sensitive electronic equipment due to lower than normal voltage, at the other end of problems there is the possibility of a fire due to overheating conductors. I'm not sure what your responsibilities are regarding leaving the installation in a safe condition (would you be required to isolate a portion of installation to bring it with the MD?)
   

Cookies
Mar 11 2020 20:20

I would say to just limit demand progressively as much as possible with fusing etc, the amount of times I’ve been concerned with demand issues and been proven wrong is ridiculous . If test results are well within the parameters and everything is as compliant as possible that’s fine and all you can do. I like to put Maximum demand mcbs at the the fuseboard for each phase where needed especially when involving large potential draws like induction jobs etc

   

Cookies
Mar 11 2020 20:22

Hobs sorry
   

nalla
Mar 12 2020 07:03

this is a very common situation, if Im inspecting on these I suggest 40amp breakers be installed on each unit.
The network are the one who benefit, their network fuse is 63amps (15kva) and the two units are have seperate ICPs so they get twice the line charges with only the one 63amp supply. Line charges are charged per ICP
You can cut the line charges back in some areas by installing a 32amp circuit breaker in the supply. There lots of houses in this area with this and have no problems with tripping.
Here you cant get cheaper line charges on 40amps you must go down to 32amps (8kva)
   

AlecK
Mar 12 2020 08:58

If there are 2 ICPs, then it's probably a case of 2 installations with separate PoSs. I say "probably" because there's no direct relationship between ICPs (or metering) and whether something is "an electrcial installation.
You need to be very clear on the point of PoS, because it changes how the Wiring rules apply.
Eg for nalla's scenario; the POCS will generally be the (63 A) supply fuse, or more accurately where the mains from that fuse crosses the boundary.
One PoS = 1 installation. After that all we need to do is ensure appropriate protection is in place. Repeated operation of overload devices is the customer's problem, not ours.

But, as a single installation, there has to be a single main switchboard that controls all of it, and has the MEN etc; with each part then fed by submains.

However IF the network has issued 2 ICP IDs, then they may (only may) have also moved the official PoS to a point somewhere downstream ; eg in a common metering position. That's 2 separate installations, with "mains" starting from each PoS.

What we can't have is
a) separate installations supplied via common; or
b) separate parts of a single installation without a common MSB.

   

Phil1605
Mar 12 2020 10:29

Thanks for the responses. Very helpful. It is all classed as 1 installation so only 1 icp. I am looking at making the meter box a main switchboard and supply each unit with a 40a mcb
   

DougP
Mar 12 2020 10:50

As it's all one installation, there must be one main switch. If the MD of the whole installation exceeds the rating of the mains, you should apply limitation, by changing the main switch to a circuit breaker.
   

YeahNah
Mar 12 2020 12:43

Is load control an option ?
Assuming 2 x HWC at 3kw each = 24amps can be loadshed.

   

MitchB
Mar 12 2020 13:40

gregmcc - I wouldn't think that this falls under the definition of "Electrically Unsafe" set out under clause 5 of the ESR's, provided circuit protection and cabling are rated correctly.