Where is Cosine based and what areas do you cover?

Cosine Electrical is based at Waerenga in the North Waikato, between Te Kauwhata and Morrinsville. We cover the wider Waikato and South Auckland — from Manukau down to Te Awamutu, east to Thames, west to Raglan. Drive times from Waerenga: Hamilton 30-40 minutes, Cambridge 40 minutes, Pukekohe 30 minutes, Manukau 45 minutes, Raglan 75 minutes, Thames 60 minutes.

What is the digger operator on the crew thing?

Most electricians sub-contract digging for underground work — second contractor, second quote, second site visit. Cosine has a skilled digger operator on the crew, so for underground jobs we trench our own runs. One quote, one team, one site visit. Note: Cosine is not a registered drainlayer. Wastewater and stormwater scope sits with a licensed drainlayer.

How quickly do you get back with a quote?

Within 24 hours of the site visit. Itemised, in writing, valid 30 days. For smaller jobs we can often give a rough indication over the phone if you text photos of the existing setup.

What does a switchboard upgrade cost?

A straight switchboard upgrade in an average three-bedroom Waikato house is typically $1,500-$2,500 plus GST for board and labour. Push-ups: old cable failing insulation tests, mains upgrade needed (lines company involvement), asbestos in the meter-box backing board common in 60s and 70s houses. Everything flagged in the written quote — no surprises on the invoice.

What does an EV charger install cost?

Standard install with the existing switchboard up to spec is $1,200-$1,800 plus GST plus the charger. Older home needing a board upgrade adds $1,500-$2,500. Long trenched runs to a detached garage on a lifestyle block typically $2,500-$4,500 all-in.

Do you do compliance testing for landlords?

Yes — landlord WOF-equivalent inspections, RCD function tests, written reports with photos and plain-English findings. Insurance-ready paperwork.

Do you work with builders on renovations?

Yes — preferred sparky for several builders across Hamilton, Cambridge and Pukekohe. We walk through with the homeowner and builder before quoting, mark up the plans, and work to the builder's schedule. We don't hold up the next trade.

Can you handle commercial maintenance for property managers?

Yes — scheduled maintenance contracts, emergency callouts, fault-finding, compliance reporting. One number, one paperwork system, no padded packages and no lock-ins.

Do you certify the work?

Always. Every new circuit and every board upgrade gets a Certificate of Compliance emailed through within a day of the job finishing. Required for insurance, future sale and any audit.

What if you cannot fix a fault in one visit?

Some faults like earth leakage on a circuit shared by multiple cables genuinely need a second visit. Day 1 we isolate the faulty section onto its own RCBO so the rest of the house keeps power. Day 2 we test and replace the bad section. We don't punch holes in walls to brute-force the search.

Getting Power to a Shed, Sleepout or Barn: What Is Actually Involved

Kris Goff

10 hours ago

3 min read

Short answer: getting power to a detached shed, sleepout or barn means running a sub-main from your main switchboard to a small distribution board in the outbuilding. The cable and the gear are rarely the expensive part. The trench is. Most jobs come down to how far it is, what the ground is like, and what has to be crossed.

The parts of the job

Work out the load. A shed with a light and two sockets is a different cable to one with a welder, a compressor and a three-phase saw bench. Undersize the sub-main and you will be living with voltage drop forever.
Size the cable for distance. Voltage drop is the thing that catches people out on a lifestyle block. A 60-metre run to the back shed needs a bigger cable than the same load 10 metres away.
Dig the trench. Buried at the depth AS/NZS 3000 requires, with the right bedding and a marker tape over the top. Deeper where vehicles cross.
Install a board at the far end. Main switch, RCD protection, circuits for lights and sockets, properly labelled.
Test and certify. Earth continuity and RCD trip times at the far end, then the paperwork.

Why the trench is the expensive bit for most people

Most electricians do not own a digger and do not operate one. So an underground run becomes two contractors: a digger crew to open the trench, then the sparky to lay the cable, then the digger crew back to backfill. Two quotes, two site visits, and you are the one coordinating them. If the weather turns between the two visits, the open trench is your problem.

We have got a skilled digger operator on the crew, so we trench our own runs. One quote, one team on site, one lot of responsibility. Worth saying plainly: we are not a registered drainlayer, so wastewater and stormwater drainage is not our scope - this is trenching for our own electrical work.

What makes a run harder than it looks

Crossing a driveway. Deeper burial and usually a conduit with mechanical protection over the top. Plan it before the driveway is poured if you possibly can.
Existing services in the way. Water, gas, fibre and irrigation lines all end up in the same corridor. Everything gets located before the bucket goes in.
Rock or heavy clay. A lot of the Waikato digs beautifully. Some of it does not. We will tell you what we hit.
Trees. Root protection zones around established trees change where the trench can go.
Sleepouts that will be lived in. If someone is going to sleep out there it is a habitable building, and smoke alarms and the associated requirements come into it - not just power.

Do it once, do it oversized

The cheapest mistake to avoid is running the smallest cable that works today. The difference between the right cable and the next size up is small money while the trench is open. Re-digging the same trench in four years because you bought a welder is not. Same goes for laying a spare conduit alongside for data or an outside light run later.

Questions we get asked

How deep does the cable have to be buried?

AS/NZS 3000 sets the minimum depths, and they change depending on whether the cable is in conduit, whether there is mechanical protection over it, and whether vehicles cross the run. For a typical domestic run it is around half a metre, and deeper under a driveway. We set the depth for your specific run and record it.

Can I dig the trench myself to save money?

Sometimes, and we will say so if it makes sense. But you would need to hit the right depth and profile, keep it open and safe until we get there, and be sure about what else is buried in that line. On most jobs the saving is smaller than people expect.

Can I run an extension lead out there instead?

For a job that lasts an afternoon, sure. As a permanent arrangement, no - a lead across the lawn is a trip hazard, it degrades in UV, and it is not protected the way a fixed installation is.

Does the sleepout need its own RCD?

Yes. The outbuilding gets its own board with RCD protection, so a fault out there does not take out the house.

Getting it priced

Tell us the distance, what is going in the building, and what the cable has to cross. That is usually enough for a realistic number over the phone before we come out. Call Kris on 021 466 666, or read more on the underground services page.