Loss of one Phase in a 3-Phase System

A 200 amp fuse blew on one leg of the 3-phase supply for office lighting and HVAC, with chaotic and destructive consequences. The AC units attempted to start off the single phase power, creating some pretty extreme sounds. We are without AC at time of posting, and I don't know whether the AC is damaged or just shut down to be inspected before returning to service. It is also possible that an AC malfunction is what triggered the event. During the event, the voltage on the blown leg fluctuated greatly, and was generally not more than 80v, according to the electrician who I talked to.

Category:

Howto & Style

Tags:

• phase
• single
• phaseing
• phasing
• power
• failure
• one
• leg
• out
• 200
• amp
• fuse
• missing
• fault
• ac
• destroyed
• odd
• unusual
• lights
• florescent
• lighting
• brownout
• wacky
• weird
• overload

[envisionelec]

Awesome commentary. :)

[asayle3r5]

@envisionelec Thanks...it was my co-worker who said that. Turns out that the fuse wire terminal in the disconnect was not getting a good connection, and the fuse would overheat and blow. It's no surprise that a few months later, they have had to replace 2 of the 3 A/C units that were affected by the failure. Motors hate single-phasing.

[viper1966]

Instead of being a jack ass with your cell phone camera and talking about glow sticks I would have got everyone to power down and find the Term Box and check which fuse is down and go get one ASAP.

But that is just me

[envisionelec]

Yes, they do. I've seen this same effect once at a big box store after a severe storm swept through and knocked a single phase out. The "digital" ballasts display interesting effects on low voltage.

[Relyas]

that's neat looking