Bubbles

Here is an interesting thing that happened today. Got a call that Main Breaker to X-Ray was kicking off so off I went. Here is how it progressed. When X-Ray was turned on after 5,15,20 min it blew main breaker (main was 100 ft away on 150 amp breaker...it didn't blow the 125amp time delay fuses 10 ft from x-ray???). We arrived and started investigating. The service is 120/208 3phase 4 wire going directly from CT into Main 800 amp panel with 3 Breakers (Load Center). It had a 225 amp 3pole feeding to a Sub-panel and a 150- 3pole feeding another sub and a 150 -3 pole feeding a dry type step up transformer (208-480) feeding to a disconnect for X-ray. The 150 amp (transformer/xray) breaker needs to stay on to keep 1/2 the lighting on in business. We isolated short in Xray (the Cathode) so left the disconnect off. Although, when you cut the 150 amp breakers only dedicated to transformer to xray..it killed a bunch of lights. Turns out when the 150amp was on all phases read 120 ground/ 208 across but, when you turn off transformer you lose phase C. Well as it turns out long story very short puco says we probably lost Phase C at transformer at street pole. Turns out we were getting a phantom voltage reading which really wasn't there. When the transformer was on it backfed phase C hence re-lighting 1/2 the building. When the x-ray tech was there he wanted to get the 480 on to test it. We said ok..hesitantly..he fired it up..and about 1 min later as we were all right there 10ft in front of it. Kaboom! Huge exposion and plume of flames came out of the anode side. He said well...it was you cathode blown..but now your anode is gone too. It was kindy funny and not at same time. I'm sure some of you have had this happen to you.

Comments and Questions

slowforthecones

how much $$$ in damage did this cause? I toasted a x-ray once before similiar sit to yours... yikes.

Bubbles

the tech said it would probably cost about 20K to repair. But, that beat 100k for a new one.

slowforthecones

So who flips the bill for this one? Hope you have great liability insurance or you can re-assign liability to the customer/previous contractor.

Bubbles

wasnt' us. we just fired up the 480 as requested by xray tech to test. I'm guessing the owner will pay. another note: the existing primary's are #2 Cu from a 150 amp 3 pole breaker to primary? and they hooked it up reverse as well (labeled as a 480-208) and using it as a step up. they have ground hooked up to the Xo.

II Weeks

was this a new install? Never ran before? Ive done a lot of Cts and MRIs and Ive heard of these things blowing up but never saw one

slowforthecones

All this could have been prevented if they had hired a licensed electrical contractor with experience in biomedical instrument installations/setups/relocs

slowforthecones

I had a few blow up in my face and I had to put out the fire too. Same as Bubbles, was called in to fire up the 480. Customer did not tell me landlord had his handyman add a new service and not a licensed electrical contractor.

Bubbles

This X-Ray was bought 5yrs ago on Ebay. It made it that long with no problems. Here is the unsolved thing to date. Local Utility still did not fix the dropped phase C to building. I'm not sure of the theory,but, does anyone know the reason that when this Transformer dedicted to the Xray is on it somehow creates a feedback through the primary (H3) back up to Bus in Main panel hence backfeeding all other panels phase C (about 20 circuits)...keeping alot of their lights on for now?? We've been on their arse for days now but their was a big windstorm that seemed to coincide with all this?? We are also thinking that if their was a power outage the huge inrush of current on the "Always in idle" mode Xray did it in.

Thanks

slowforthecones

Have you looked at the transformer on the street parking lot? got a pic of some of this?