Online assistance for electrical trade people in New Zealand and Australia Login  |  Register  |   Forgot Password
Assistance for electrical trade people




Click here to send Ron a pdf document for publication on this Topic

Documents must be less than 200k in pdf format

Posted By Topic: Do I Need a CoC?

Nov 08 2018 09:31


I am a registered electrician, retired 10 years ago due to health. All OK now. Own our home, but I don\'t have active registration.

I am planning to add solar generation. And I allowed to do this work on my own premises? Supply Authority wants to see a CoC, do I need that for work on my own place?

I know in the past I did not, but looking at regs etc., I cannot see an exemption now.



Nov 08 2018 09:43

Always needed a CoC (since Cocs were introduced).
But used to be an exemption from needing a Practising Licence, if registered but not working for hire / reward.
It was abolished some years ago.

So short answer is you are not allowed to do it on your own premises unless you obtain a PL - this sort of work\'s well beyond what the \"homeowner exemption\" allows for.

There haven\'t been \"Supply Authorities\" since 1993, but if the network operator wants a CoC I\'m guessing this is a grid-connected system. And yes they will want to be certain that you\'re doing it correctly. Among other things; they don\'t want back-feeding onto the lines when their staff are working on them during outages.

A grid-connected system is also classed as \"high risk\" work, so will need to be inspected before being connected.
And if the PV array has an open-circuit voltage above 120 V (making it LV instead of ELV); that\'s \"high risk\" work also, so another inspection needed.

Nov 08 2018 15:00

Unrelated to the question, but if you have the space to erect an overcapacity of panels then definitely check out option of going off-grid with batteries.

NZ\'s buy-back scheme makes staying on-grid unattractive if you\'ve got the money and space to go the extra step.


Nov 08 2018 19:36

Not sure if going of grid is cost effective . If it was everyone would do it . Buy back tariff is still about the same as the energy retailer pays .
Off grid is only effective when you are in the country and have to pay for long cable runs and possibly pay for a transformer.

Nov 08 2018 19:42

It would be better to invest in solar water heating if you haven\'t already done so.

Nov 08 2018 20:06

Or a heat pump water heater ..... Wow now were compleatly off the original posters Question!

Nov 08 2018 23:14

Grid-tie PV is not cost effective, for sure.


Nov 09 2018 06:43

Can be if the consumer is at home using power during the day wh8ile it\'s being generated.
And since the OP is retired,it may well be for him.
Whereas the investment for batteries to enable load-shifting is significant; and the pay-back correspondingly longer.

Nov 09 2018 09:17

Thanks for all the responses. I have decided to get a practising license, I have some mains and switchboard work to do here.

Some more info...

I have acquired an approved Grid Tie inverter for less than 10% of retail. I expect to feed it with a mix of solar and wind. Solar PV\'s need to get to 50c a watt before I would consider them really viable for full off grid when grid is currently available. Same with batteries, they are just not cost effective, their price will buy a lot of grid power.

End game is to have play and shave about 30% off our current power bill with minimal investment.

Nov 09 2018 10:51

Alec notes:

> Can be if the consumer is at home using power during the
> day wh8ile it\'s being generated.

This is the important bit; exporting power to the grid for 8c/KWH is a mugs game. One needs to use every watt generated, and thus get the full retail value of one\'s generation.

For most folks in Kiwiland, with electrically heated water and a tank with reasonable capacity, the way to do this is a diverter, so that any unused solar watts go into the hot water, and then top off the tank with street power once the sun goes down.


Nov 09 2018 14:54

6 cents in summer time.


Nov 09 2018 14:57

And remember, they take away your split night/day option too. So, when getting grid-tied, expect your night units to hurt more.


Nov 09 2018 15:01

As in double the cost.


Nov 11 2018 19:30

PV Solar in my house Only heats the water. 4 panels connected directly to the cylinder through a volt sensing relay. Thats my battery.

Nobody home through the day so absolutely No point connecting it to anything else.

But even though Ive paid bugger all to Contact for hot water in last two years, its still only marginally cheaper when calculating the capital cost over life expectancy.

Nov 12 2018 00:36

SymonS am pretty interested in what you\'re doing. If you\'ve got 4 panels (assume in series), then you\'ll get 0-50v -ish out of them. Are you DC-AC inverting them up to 230v or what? I\'ve been pondering this for a few years but I reckon on putting at least 8 panels in series. Why a relay when the thermostat will deal with over-heating or is the relay for current dumping into a dummy load?

Nov 12 2018 10:27

Sounds like he\'s got the relay switching in the panels, to the single 230v element, when volts appear on the panels.

The four panels will be 24 volt types, probably peak of 250 Watts each, and all connected in series. For a 3 kW element, this could provide up to maybe 6.5 Amps at 110 Vdc, or 715 Watts of heating.


Nov 12 2018 10:32

Energising the relay directly from the panel voltage might be unreliable given the voltage can be highly varied. Probably want more hysteresis than an average magnetic coil will provide.


Nov 12 2018 10:36

Make sure you are aware of the implications of the level of voltage here and PEW and switching currents who\'s arcs don\'t self extinguish 50 times a second.
I\'ve seen several proud posts on other forums where this was not understood - I\'m sure it is here but for those reading and getting ideas.

Nov 12 2018 13:18

All you really need it for the thermostat to switch the supply from the panels. Obviously via a suitably rated relay to switch the DC. It doesn’t matter if the panels are getting sun or not. As soon as the sun is available and the thermostat is calling for heat current will flow in the element circuit. When the cylinder gets up to temp the thermostat will switch off the relay and open circuit the panels. No problems and simple as.

Nov 15 2018 12:18

as long as you use a t'stat / relay with a suitable DC rating. AND maintain full segregation between the LV ac and the ELV / LV dc.

Nov 15 2018 19:39

Is there any point providing a tstat? Direct solar systems generally just heat until it boils and rely on the overflows.

There's no reason to stop at 60C if power is free, and it lets you cram more energy into the tank at the cost of higher losses.

Nov 15 2018 23:13

Just a note on a "suitably rated relay" - One frequently sees relays with headline specs like AC 10A 250V, DC 10A 125V, but be aware, such relays are often not rated for 10A at 125VDC; there are derating curves in the relay data sheet, so it may do 10A at 30VDC, but as the voltage goes up the current rating goes down.


Nov 16 2018 22:05

If the tank is unvented; it's basically a bomb and MUST have manual reset over-temp as well as an operational t'stat.

And there are other Building Code requirements such as not delivering water ex-tap at more than 60 deg C ; so if taking in more energy need to ensure there's a tempering valve fitted (and working).