C
Crustycracker
At my site I have 3 x Danfoss VLT6000 motor inverters for our pumps. The MCB's have always been warm to touch and as they were put in by a contractor before I came to site I assumed it must be correct.
As late the 25A rated 3 pole MCB's were detected by a thermal image survey as being too hot. I investigated this further. I found each MCB casing had become slightly brittle and brown at the sides and also the 6mm singles at the terminal ends and up to 3" out had brittle insulation. I did a clamp test and each circuit was carrying around 23A on full load. Although the inverter display told me 27A. I had the singles replaced, max. 8mt run in steel 3" trunking. I replaced the first two MCB's with 32A MCB's thinking that the old 25A's where probably a bit close to the mark. During the replacement of the second set of pump cables I noticed that the new 32A MCB was running just as hot. I rechecked the current in the singles cables which was still about 23A. Absolutely puzzled I contacted Danfoss on this problem. I was pointed to a page on their web site about installation of the inverters. The installation at my site was miles away from what Danfoss installation instructions required. Danfoss siad use screened cable and also use cartridge fuses. I had singles in trunking, although no overcrowding whatsoever, and MCB's. The guy at Danfoss did his utmost to explain to me what he believed to be the problem mentioning harmonics, cable resistance even low currents, etc. etc. It was over my head I'm afraid. Shortly after I contacted Merlin Gerin (what a nightmare that was, I hate Schneider, they are like Tesco's...too big and fat). A helpful chap said that in his experience MCB's can run warm without a problem but I couldn't specify the temperature of mine at that point. But I have since checked....MCB's old and new ones are running at 51 degrees and cable temp along entire length is about 35 degrees. I am certainly unhappy with this. I have left the trunking lid off for now and the MCB's have plenty of space around them in the D/B.
I am at a loss at how to tackle this so am looking for another bright spark who may have installed the same or similar in the past and has had the same issues. I have never installed inverters myself in my years but have maintained sites with them in use. Even now I am not that familiar with them apart from knowing that they can save energy.
Any thoughts anybody???
As late the 25A rated 3 pole MCB's were detected by a thermal image survey as being too hot. I investigated this further. I found each MCB casing had become slightly brittle and brown at the sides and also the 6mm singles at the terminal ends and up to 3" out had brittle insulation. I did a clamp test and each circuit was carrying around 23A on full load. Although the inverter display told me 27A. I had the singles replaced, max. 8mt run in steel 3" trunking. I replaced the first two MCB's with 32A MCB's thinking that the old 25A's where probably a bit close to the mark. During the replacement of the second set of pump cables I noticed that the new 32A MCB was running just as hot. I rechecked the current in the singles cables which was still about 23A. Absolutely puzzled I contacted Danfoss on this problem. I was pointed to a page on their web site about installation of the inverters. The installation at my site was miles away from what Danfoss installation instructions required. Danfoss siad use screened cable and also use cartridge fuses. I had singles in trunking, although no overcrowding whatsoever, and MCB's. The guy at Danfoss did his utmost to explain to me what he believed to be the problem mentioning harmonics, cable resistance even low currents, etc. etc. It was over my head I'm afraid. Shortly after I contacted Merlin Gerin (what a nightmare that was, I hate Schneider, they are like Tesco's...too big and fat). A helpful chap said that in his experience MCB's can run warm without a problem but I couldn't specify the temperature of mine at that point. But I have since checked....MCB's old and new ones are running at 51 degrees and cable temp along entire length is about 35 degrees. I am certainly unhappy with this. I have left the trunking lid off for now and the MCB's have plenty of space around them in the D/B.
I am at a loss at how to tackle this so am looking for another bright spark who may have installed the same or similar in the past and has had the same issues. I have never installed inverters myself in my years but have maintained sites with them in use. Even now I am not that familiar with them apart from knowing that they can save energy.
Any thoughts anybody???
