ungrounded 3 phase systems

[reckoner4160]

hello. looking for advice on working on a 3 ph, 3 wire 480 delta that i believe fits the definition of a corner grounded delta. the title of the thread is appropriate because theres only 3 wires marked for each phase and no neutral going into the customers main disconnect switch which powers a 3 phase 480v motor control circuit.
i say its corner grounded because there appears to be a bonding strap tying the middle phase conductor to the meter enclosure but am puzzled at why its bonded at that location especially when the manufacturer's label states specifically, "When service is not grounded, remove [this] bonding strap..."
i think the meter enclosure was intending for the middle conductor to be a neutral (a grounded system) but in this case its not (3 wire, 3 phase delta) or at least not supposed to given the customers requirements for a 3 ph 480v motor.
so my question is where is the proper place to ground a phase conductor? at the pole or pad mounted transformer? at the customer's first disconnect? or at the meter or anywhere else?

i will post pictures as soon as i can figure out how to do so.

 

[westward10]

Thank you for reposting the best person to answer this is @Megawatt when he picks up on this.

 

[reckoner4160]

adjusted the tint here to make the red label more legible which reads "When service is not grounded remove bonding strap re-install screw"

notice how its grounded here

 

[Megawatt]

hello. looking for advice on working on a 3 ph, 3 wire 480 delta that i believe fits the definition of a corner grounded delta. the title of the thread is appropriate because theres only 3 wires marked for each phase and no neutral going into the customers main disconnect switch which powers a 3 phase 480v motor control circuit.
i say its corner grounded because there appears to be a bonding strap tying the middle phase conductor to the meter enclosure but am puzzled at why its bonded at that location especially when the manufacturer's label states specifically, "When service is not grounded, remove [this] bonding strap..."
i think the meter enclosure was intending for the middle conductor to be a neutral (a grounded system) but in this case its not (3 wire, 3 phase delta) or at least not supposed to given the customers requirements for a 3 ph 480v motor.
so my question is where is the proper place to ground a phase conductor? at the pole or pad mounted transformer? at the customer's first disconnect? or at the meter or anywhere else?

i will post pictures as soon as i can figure out how to do so.

All I can tell you that on a 3 phase delta system and the middle phase should be marked with orange tape meaning that the middle phase has much higher voltage. I’m not sure how you got a 3 phase delta service but I have never heard bonding the middle phase. Read with you meter on each phase to ground with the jumper wire removed and if I’m right you should read 120vac on phase A and C and phase B is going to be around 150vac

 

[Megawatt]

adjusted the tint here to make the red label more legible which reads "When service is not grounded remove bonding strap re-install screw"View attachment 93163

notice how its grounded here View attachment 93164
View attachment 93165

By looking at that picture take that strap off. Very odd looking 3 phase service. Are you absolutely sure it’s 3 phase ?

 

[reckoner4160]

All I can tell you that on a 3 phase delta system and the middle phase should be marked with orange tape meaning that the middle phase has much higher voltage. I’m not sure how you got a 3 phase delta service but I have never heard bonding the middle phase. Read with you meter on each phase to ground with the jumper wire removed and if I’m right you should read 120vac on phase A and C and phase B is going to be around 150vac

its a 3 phase 3 wire system. line to line reads 480v across all 3 wires.
line to ground measurements is where it gets weird. A phase (labeled as x phase in the pic) to ground is 480v, C phase (labeled as z phase) to ground is also 480v. B phase (the middle phase in the pic) to ground is zero volts. you read that right. zero volts. that should tell any electrician worth his or her salt that that conductor is grounded. if you notice the ground wire is marked with white tape to signify it as a grounded conductor when its really the equipment grounding conductor since its attached directly to the pole ground outside the meter box. looking at all this i'm amazed the customer has had no electrical issues. judging by the size of the wires one can assume they don't draw a heavy load despite the 480v rating of the motors, but that's not my concern...

I believe B phase conductor needs to be marked as a grounded conductor to signify to any future electrician troubleshooting this service that it is such. I also have a problem with how its grounded-- that tiny ground screw is not meant for installing a ground wire. its there to ground the meter to the case as you can see in the pics. now there's a case ground lug located directly below and to the right of the meter (behind the red handle of the bypass lever). but proper equipment grounding isn't the real issue here. its how and why one of the phase conductors is grounded whether intentionally or not at that location.

 

[reckoner4160]

All I can tell you that on a 3 phase delta system and the middle phase should be marked with orange tape meaning that the middle phase has much higher voltage. I’m not sure how you got a 3 phase delta service but I have never heard bonding the middle phase. Read with you meter on each phase to ground with the jumper wire removed and if I’m right you should read 120vac on phase A and C and phase B is going to be around 150vac

i forgot to mention that on a 4 wire, 3 phase delta if you read 120v phase to ground on any two lines then your third phase would actually read 208v. but yes that high leg should be marked as such on the customers main disconnect. i've seen quite a few of these 3 wire 3 phase ungrounded delta and they all read 490+ line to line, and roughly 240v-290v on any line to ground (voltage fluctuating because there's no neutral). on this service however you get a very solid 480v line to line and also to ground except B phase. its perfectly legal and safe (but not in this case i think) and is used for a very narrow application. i hear they are trying to move away from these ungrounded systems.

the bonding of the middle phase in this meter enclosure was intended, i believe, for a single phase 3 wire service where the middle conductor is the neutral. this actually applies to all standard single phase 3 wire residential services in the US-- with the neutral bonded at the meter socket (usually directly behind the meter in older homes with a 100 amp or less rated main)

 

[Megawatt]

i forgot to mention that on a 4 wire, 3 phase delta if you read 120v phase to ground on any two lines then your third phase would actually read 208v. but yes that high leg should be marked as such on the customers main disconnect. i've seen quite a few of these 3 wire 3 phase ungrounded delta and they all read 490+ line to line, and roughly 240v-290v on any line to ground (voltage fluctuating because there's no neutral). on this service however you get a very solid 480v line to line and also to ground except B phase. its perfectly legal and safe (but not in this case i think) and is used for a very narrow application. i hear they are trying to move away from these ungrounded systems.

the bonding of the middle phase in this meter enclosure was intended, i believe, for a single phase 3 wire service where the middle conductor is the neutral. this actually applies to all standard single phase 3 wire residential services in the US-- with the neutral bonded at the meter socket (usually directly behind the meter in older homes with a 100 amp or less rated main)

A true 480 volt 3 phase delta service should read phase to ground at 277 volt and phase to phase is 480 volts. I have never seen a 480 3 phase service run to a single family dwelling. How are you getting 120 for the receptacles and lights, 220 volt for dryer, stove, heat and air conditioning?