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Serviceman's Log

Many homes have had solar panels installed over the last few years, usually ranging from about 1.5kW up to 4kW. But how safe are they, especially if they have been installed in a rush to meet subsidy deadlines?

by the Serviceman

Items Covered This Month

• The solar panel system that almost caught fire

• White goods jinx

• NEC PXT42XD2 106cm plasma TV

• Lafayette HE-30 communications receiver

• Intermittent ECU in Rover 3500SE

*Dave Thompson, runs PC Anytime in Christchurch, NZ.

This month, I’m kicking off with an interesting story from P. W. of Hope Valley, SA. He recently had a rather worrying encounter with a solar panel installation that nearly caused a fire. Here’s how he tells it . . .

We recently had a 1.5kW solar system installed on our home and shortly after, our neighbour installed a 3kW system. In each case, the inverter was installed adjacent to the external meter box at the front corner of the house. In fact, both inverters and their associated LCD readouts were visible when standing alongside my meter box.

Being interested in the system’s performance, I soon got into the habit of reading and recording the solar energy meter and the network import/export meter for my installation at about the same time each day. And because it was adjacent, I also occasionally compared the daily output of my system with that of my neighbour’s.

One day, however, I noticed that his system had shut down. I duly knocked on his door to let him know this and together we attempted to restart the system. We opened the AC solar system circuit breaker and then the adjacent DC isolator and then attempted to restore them in reverse order. The only obvious problem was that the DC isolator would not remain in the open position and would immediately spring back to closed when released. The inverter also seemed to attempt to start up, with indications from the LCD panel, but would shut down after a few seconds.

In the end, it looked like there was some sort of fault with the inverter’s DC isolator, so I left my neighbour who was now intending to phone the installer for a warranty call-out. About 30 minutes later, however, he came in and said that he had climbed onto his roof to inspect the panels and had detected a strong odour that smelt like burnt electrical equipment. And he asked whether I could help him out as he knew that I had skills in this area.

I climbed onto the roof with him and confirmed that the smell came from the vicinity of the roof-top solar panel DC isolator. The plastic box was quite hot to the touch and as we were inspecting it, the sun came out from behind a cloud, providing full solar energy. That gave us our first real clue because we now observed wisps of smoke coming from around the gland where the cables from the panels entered the box.

We immediately opened the isolator but the switch mechanism felt rather vague, rather than giving a positive clunk. By this stage, I was quite concerned about the smoke and suggested that my neighbour bring his portable fire extinguisher up immediately. This was done and we then contemplated what to do next. Clearly, the panels were not yet isolated and I thought it unwise to open the inter-panel socket connectors under load.

This was further complicated by the fact that the solar array was connected in two strings and the lower string connectors were somewhere under the panels and could not be reached from any side.

In the end, I suggested that we cover the panels with drop sheets to remove the solar energy source before opening the plugs. This was quickly achieved and the accessible top section was easily unplugged.

The lower section needed one panel to be slid down to access the plugs. As a result, a hex key was used to loosen the mounting screws, after which the panel was slid down and the lower section of the array unplugged

Now that the panels were electrically isolated and fire-safe, we removed the lid from the DC isolator box to be greeted with a blackened, melted, stinking mess. The isolator switch itself was a 4-pole unit, with the two pairs of DC solar panel cables paralleled into two of the poles at one end and the positive and negative cables to the inverter exiting the other two poles from this same end.

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