# 480v Compressor Contactor How?



## OSB_Electro (Sep 8, 2021)

Hey everyone. I have a question and I know the answer is most likely something simple but y damn brain is just not clicking today. We have a 480v 3 phase 80Gal compressor I assume that the internal contactor would utilize a leg of 277v to pull in the motor starter coming from the pressure switch but on A1 is 277v and A2 is 277v how is this not a dead short Phase to Phase? Appreciate the comments


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## oldsparky52 (Feb 25, 2020)

You are assuming?... I would look a lot harder to be sure.

Were you reading voltage from A1 to ground and A2 to ground? What were the voltages from A1 to A2?

The mods will want you to fill out your profile. I suggest you do that.


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## OSB_Electro (Sep 8, 2021)

oldsparky52 said:


> You are assuming?... I would look a lot harder to be sure.
> 
> Were you reading voltage from A1 to ground and A2 to ground? What were the voltages from A1 to A2?
> 
> The mods will want you to fill out your profile. I suggest you do that.


A1 277v to Ground 
A2 277v to Ground
A1 to A2 480V

I haven't physically gone out into the field to verify because I am currently off-site. Just going by what one of my guys said.


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## just the cowboy (Sep 4, 2013)

No you have a 480 volt contactor coil, not uncommon when control voltage don't leave enclosure.


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## OSB_Electro (Sep 8, 2021)

OSB_Electro said:


> A1 277v to Ground
> A2 277v to Ground
> A1 to A2 480V
> 
> I haven't physically gone out into the field to verify because I am currently off-site. Just going by what one of my guys said.


Were used to seeing Phase to Neutral contactors this just happens to be a Phase to Phase contactor which is defiantly unique in our industry.


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## micromind (Aug 11, 2007)

The reason line-to-line is used is because there's no need to pull in a neutral. 

Line-to-line controls are pretty common around here.


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## John Valdes (May 17, 2007)

Most all combination starters use line voltage for pilot and control.


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## paulengr (Oct 8, 2017)

OSB_Electro said:


> Were used to seeing Phase to Neutral contactors this just happens to be a Phase to Phase contactor which is defiantly unique in our industry.


That’s very strange and something I’ve never seen.

Motors don’t need a neutral at all. Regardless of the internal wiring it’s a delta load.

With full voltage controls if they were designed for a neutral you would need an extra neutral for everything and have to wire it up 4 wire wye. So the manufacturers would need to stock both a 3 wire version for say customers running 3 wire delta and a 4 wire wye version. Or just keep only a 3 wire delta version on the shelf.

That being said 480 V controls these days are kind of frowned on for safety reasons. A push button that arcs and fails tends to come flying apart and freaks out operators. So over time the pre 1970s style of using 480 V control wiring has been slowly disappearing along with having only two overloads. The most common approach is to incorporate a small say 150 VA control power transformer with fuses into the bucket and use 120 VAC controls. Since the bucket contains it’s own separately derived system if the secondary is grounded to the frame then the grounded phase is a neutral and uses white wiring but most just use all red or all black.

I have seen a 277 coil maybe once a decade. Almost all coils are 120, 208/230, or 480. Once in a while on more recent systems I might also see 24 or 48 V and in power plants 48, 125, or 250 VDC might be used. 277 would be extremely rare.


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## 460 Delta (May 9, 2018)

paulengr said:


> That’s very strange and something I’ve never seen.
> 
> Motors don’t need a neutral at all. Regardless of the internal wiring it’s a delta load.
> 
> ...


One other way that is common at least in r-mix on local control motors (water pumps, compressors) is a neutral and A or C phase used for 120 volt control. Works great until someone gets confused and lands B phase as control.


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## SteveBayshore (Apr 7, 2013)

I have never installed a combination starter with a 480 volt coil. ALWAYS install a small CPT with fuses and 120 volt coils, even of control wiring doesn't leave the enclosure. I have had to work in old plants that have 480 remote controls. Each starter has a small fuse block to protect the control conductors going to a control panel. Then you open up a control panel with 40 or so operators, all with 480 volt wiring on the back. Pretty nasty to troubleshoot.


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## just the cowboy (Sep 4, 2013)

SteveBayshore said:


> I have never installed a combination starter with a 480 volt coil. ALWAYS install a small CPT with fuses and 120 volt coils, even of control wiring doesn't leave the enclosure. I have had to work in old plants that have 480 remote controls. Each starter has a small fuse block to protect the control conductors going to a control panel. Then you open up a control panel with 40 or so operators, all with 480 volt wiring on the back. Pretty nasty to troubleshoot.


Especially on a corner grounded system and the door wants to swing shut.


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## SteveBayshore (Apr 7, 2013)

I've always been timid with corner grounded systems. My first experience was in a new factory in the 80s that made commercial/industrial cooking equipment. They needed 200 amp test panels for as many voltages that would be available at their customers sites. The utility service was 277/480 volts in the factory and we set dry transformers for the voltages as directed by their in house EE. We had a 150 kva 480 delta by 480 delta secondary transformer and he wanted one of the load phases grounded. No one wanted to be the one to turn on the breaker feeding the transformer with that piece of 1/0 connected to the load phase and to the ground bar. Huh, power on and no bang, I almost didn't believe it. Did the same thing only with a 240 volt secondary transformer also. I have only worked on a couple of other systems since then.


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## just the cowboy (Sep 4, 2013)

When I worked in the shipyard everything 480 volt was corner grounded. They did it so the power house had time to transfer power then find the fault so 1,000's of machines did not shut down and cause $$$$$$$$ of scrap metal. 
Since a lot of the machines were from the 40-50's they were 480 controls. Had a door swing closed and reflexes pushed it open, but I hit a PB contact and ground and put a small hole in my hand where it went in.


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## SteveBayshore (Apr 7, 2013)

just the cowboy said:


> When I worked in the shipyard everything 480 volt was corner grounded. They did it so the power house had time to transfer power then find the fault so 1,000's of machines did not shut down and cause $$$$$$$$ of scrap metal.
> Since a lot of the machines were from the 40-50's they were 480 controls. Had a door swing closed and reflexes pushed it open, but I hit a PB contact and ground and put a small hole in my hand where it went in.


Was that corner grounded delta or ungrounded delta? I didn't know that a corner grounded delta acted like an ungrounded delta. I'll have to think about this.


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## just the cowboy (Sep 4, 2013)

SteveBayshore said:


> Was that corner grounded delta or ungrounded delta? I didn't know that a corner grounded delta acted like an ungrounded delta. I'll have to think about this.


I'll have rethink it too.  It was 40 years ago


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## 460 Delta (May 9, 2018)

just the cowboy said:


> I'll have rethink it too.  It was 40 years ago


Maybe a resistance ground?


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## micromind (Aug 11, 2007)

just the cowboy said:


> When I worked in the shipyard everything 480 volt was corner grounded. They did it so the power house had time to transfer power then find the fault so 1,000's of machines did not shut down and cause $$$$$$$$ of scrap metal.
> Since a lot of the machines were from the 40-50's they were 480 controls. Had a door swing closed and reflexes pushed it open, but I hit a PB contact and ground and put a small hole in my hand where it went in.


Most likely it was high-impedance grounded. The main reason for this system is reliability. The first ground fault, even a bolted fault does not cause anything to trip, it simply causes some sort of indication that there's a ground fault. 

The second ground fault is a different story........it's phase-to-phase..........something will either trip or blow up...........


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## mburtis (Sep 1, 2018)

We have an ungrounded 240 system. Why I have no clue but I check the lights everytime I walk by them. Read an article once where it was talking about burning out like 50 motors in 2 hours because of 2 faults on a ungrounded system.


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## paulengr (Oct 8, 2017)

mburtis said:


> We have an ungrounded 240 system. Why I have no clue but I check the lights everytime I walk by them. Read an article once where it was talking about burning out like 50 motors in 2 hours because of 2 faults on a ungrounded system.


It’s in one of the IEEE standards on grounding.

Impedance grounding is very safe. You get all the advantages of an ungrounded system (easy to trace faults, minimal damage, optional alarm only) and none of the disadvantages (transients).

The IEEE grounding standard talked about burn down. If you have ground faults on 2 phases it’s not phase to phase. It is far worse because it’s phase-ground-phase which usually won’t trip because of the high fault impedance and causes ground potential rise.

That being said I’m more inclined to believe that this was an arcing fault. On an ungrounded system with an arcing fault you get very high (600-800% of line-line voltage) and it quickly shreds other equipment if gone unchecked.


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