The case of the missing Phase.... - 01/16/06 09:25 PM
Had a good one recently... some background first:
My brother-in-law owns a hair salon, located in a shopping center storefront. Service is provided via a large padmount with UG feeders to a meter bank with meters and disconnects for each tenant. The panels in each storefront are cringe Zinsco three-phase. Several years (15 or so) ago, I rewired his entire shop, trying to balance the continuous loads (hair dryers, etc.) on the three phases. I must have done something right, as one time there was a brownout in the area. My shop stayed on, while a competitor's shop in the same center had their panel literally explode. (According to my B-I-L, the electrician sent to repair the other shop's panel looked at mine to figure out how we dodged the bullet.)
Anyway, last week he called to say that they had lost some power. Some plugs and lights were dead and the A/C wasn't working. The lights in the bathroom would come on and off randomly but at half-bright. Huh? My first thought was that a neutral was lost, but I remembered that I ran dedicated neutrals for every circuit. If the main neutral had gone there'd be more smoke that lights for sure.
I suggested that he turn the breaker for the A/C off, as his old unit had failed and caused a similar problem, dragging a phase low but not tripping the breaker. (Zinsco, remember?) He shut the A/C breaker off, now the lights in the bathroom went out conpletely! I told him I'd come check it out.
When I arrived I checked the panel first, thinking maybe "Zinsco-itis" had struck. Nope, the busses were o.k. Metered the main lugs, and the B phase was floating around 50 volts. A and C phases 120-124 with load. Hmm. Went out back to the disconnect. Found old-looking fuses of a type I'd never seen before (Gould OT-80). Metered load side of fuses, A phase 120, B phase 120(?) C phase 50 {yep, when the disconnect was replaced someone switched the B and C phases.) Line side of fuses same results. Well, maybe it's the actual switch itself. The line lugs were well protected and hard to get to with the meter probes safely, so I stood up (bumping my head on the electronic POCO meter)to go inside to tell my B-I-L I need to shut all the power off to cycle the disconnect switch. (Thinking bad contacts.) As I walked in, I noticed the bathroom lights were on full. WTH?
I had them try the "dead" recepts, which were now working....strange. So I went to the panel and threw the A/C breaker on...it started up for about 3 seconds and then shut down...and so did the recepts and bathroom lights again.
I'm gonna stop here and see if you guys figure out what was happening. I'll follow up with the answer later!
My brother-in-law owns a hair salon, located in a shopping center storefront. Service is provided via a large padmount with UG feeders to a meter bank with meters and disconnects for each tenant. The panels in each storefront are cringe Zinsco three-phase. Several years (15 or so) ago, I rewired his entire shop, trying to balance the continuous loads (hair dryers, etc.) on the three phases. I must have done something right, as one time there was a brownout in the area. My shop stayed on, while a competitor's shop in the same center had their panel literally explode. (According to my B-I-L, the electrician sent to repair the other shop's panel looked at mine to figure out how we dodged the bullet.)
Anyway, last week he called to say that they had lost some power. Some plugs and lights were dead and the A/C wasn't working. The lights in the bathroom would come on and off randomly but at half-bright. Huh? My first thought was that a neutral was lost, but I remembered that I ran dedicated neutrals for every circuit. If the main neutral had gone there'd be more smoke that lights for sure.
I suggested that he turn the breaker for the A/C off, as his old unit had failed and caused a similar problem, dragging a phase low but not tripping the breaker. (Zinsco, remember?) He shut the A/C breaker off, now the lights in the bathroom went out conpletely! I told him I'd come check it out.
When I arrived I checked the panel first, thinking maybe "Zinsco-itis" had struck. Nope, the busses were o.k. Metered the main lugs, and the B phase was floating around 50 volts. A and C phases 120-124 with load. Hmm. Went out back to the disconnect. Found old-looking fuses of a type I'd never seen before (Gould OT-80). Metered load side of fuses, A phase 120, B phase 120(?) C phase 50 {yep, when the disconnect was replaced someone switched the B and C phases.) Line side of fuses same results. Well, maybe it's the actual switch itself. The line lugs were well protected and hard to get to with the meter probes safely, so I stood up (bumping my head on the electronic POCO meter)to go inside to tell my B-I-L I need to shut all the power off to cycle the disconnect switch. (Thinking bad contacts.) As I walked in, I noticed the bathroom lights were on full. WTH?
I had them try the "dead" recepts, which were now working....strange. So I went to the panel and threw the A/C breaker on...it started up for about 3 seconds and then shut down...and so did the recepts and bathroom lights again.
I'm gonna stop here and see if you guys figure out what was happening. I'll follow up with the answer later!