Does anyone use GFCI breakers on their CNC machines?

[steve-l]

OK, I have still not found a single GFCI breaker that is 240V/3Ph!
There are plenty under 50 A ( max required by NEC ), but they are all for 208V systems, which automatically means 208/120 Wye with Neutral.

Does anyone have any links to a true GFCI device for Delta services?

Steve ...
From what I saw, at this time NEC only requires GFCI for :
L-Ground voltages below 150V
Current of 50A or less for single phase, 100A or less for 3 phase
Receptacle connections only ( hard wired connections do not require GFCI )

Thanks for that info. In Germany the power from the street is 400 V 3 phase. The GFCI breaker is installed right after the meter and it monitors all loads powered by that electrical service. I repeat "ALL" loads, including welders. I also have a 25 KW 400 V generator in a container that feeds my house and shop as well as my neighbor's house. That generator also uses two separate GFCI breakers. one for each load. This arraignment works fine and covers all loads wye, delta, single phase, receptacles or hard wired. Only one breaker is required per power feed. It works well. These are installed at the junction box containing separate bus bars for all 3 phases , neutral and safety earth and where the bond between safety earth and neutral is made.

 

[SeymourDumore]

Thanks for that info. In Germany the power from the street is 400 V 3 phase. The GFCI breaker is installed right after the meter and it monitors all loads powered by that electrical service. I repeat "ALL" loads, including welders.
....
This arraignment works fine and covers all loads wye, delta, single phase, receptacles or hard wired.

Steve, Yes, that is the European system.
I grew up there with the 220/380 in the mid 80-s, which is now 230/400.
In all cases, it is always a 3ph/Wye service, and in all cases includes a Neutral in the service panel.
A GFCI at the MAINS will in fact provide protection for all loads downstream, as the Neutral is referenced to Wye center, which is also Ground, and your GFCI breaker monitors the Neutral conductor.

In the US, there certainly is an equivalent to the European, one of which is the 208/120 Wye service.
In this case the GFCI at the MAINS would protect the same way it does over there.

The other equivalent service is the 277/480 Wye supply.
In this case the NEC code with respect to GFCI does not apply as the Line-Ground voltage is 277V, which is above the 150V threshold.

Finally, we get to the typical industrial 240V Delta supply.
There is no Neutral to reference to, so what would the GFCI breaker be comparing to?

Aaaaannnnnndddd..... I am leaving out all the other abominations of services in the US.....

 

[sfriedberg]

Finally, we get to the typical industrial 240V Delta supply.
There is no Neutral to reference to, so what would the GFCI breaker be comparing to?

I'm repeating myself. I promise this is the last time I will say it. A GFCI breaker does not care whether "hot" wires are supply or neutral/return. It sums the current across all the hot wires, and trips if the sum is not (almost exactly) neutral. If you have 3-wire Delta service, the GFCI breaker sums the currents on those three wires. If you have 4-wire Wye service, the GFCI breaker sums the currents on those four wires. If the sum across all the hot wires is not zero, it means some current is taking a path that does not involve only those 3 (only those 4) wires, and this is considered a fault.

Technically, a GFCI fault needn't be a ground fault. Leakage from a hot wire of one branch circuit returning via a different branch circuit will also trip a GFCI breaker.

The equipment grounding conductor ("green wire") is, by design, not a hot wire.

 

[steve-l]

Steve, Yes, that is the European system.
I grew up there with the 220/380 in the mid 80-s, which is now 230/400.
In all cases, it is always a 3ph/Wye service, and in all cases includes a Neutral in the service panel.
A GFCI at the MAINS will in fact provide protection for all loads downstream, as the Neutral is referenced to Wye center, which is also Ground, and your GFCI breaker monitors the Neutral conductor.

In the US, there certainly is an equivalent to the European, one of which is the 208/120 Wye service.
In this case the GFCI at the MAINS would protect the same way it does over there.

The other equivalent service is the 277/480 Wye supply.
In this case the NEC code with respect to GFCI does not apply as the Line-Ground voltage is 277V, which is above the 150V threshold.

Finally, we get to the typical industrial 240V Delta supply.
There is no Neutral to reference to, so what would the GFCI breaker be comparing to?

Aaaaannnnnndddd..... I am leaving out all the other abominations of services in the US.....

You seem to not understand that the GFCI to function in a DELTA example does not need Neutral. The current comparison is phase to phase. Neutral is used in the comparison in both a single phase and a wye example. In point of fact circuit voltage is irrelevant other than the insulation of its construction. These devices work in all examples and they work well.

 

[gustafson]

Thanks for that info. In Germany the power from the street is 400 V 3 phase. The GFCI breaker is installed right after the meter and it monitors all loads powered by that electrical service. I repeat "ALL" loads, including welders. I also have a 25 KW 400 V generator in a container that feeds my house and shop as well as my neighbor's house. That generator also uses two separate GFCI breakers. one for each load. This arraignment works fine and covers all loads wye, delta, single phase, receptacles or hard wired. Only one breaker is required per power feed. It works well. These are installed at the junction box containing separate bus bars for all 3 phases , neutral and safety earth and where the bond between safety earth and neutral is made.

While this may be code there, what a dumb idea


hey let's try to troubleshoot a ground fault when the entire service for the building is out.

Let's shut down an entire CNC machine shop because one circuit on one sub panel has an intermittent fault


9 hours into a 9 hour 3 minute surfacing pass the power shuts off and trashes the part

 

[mmurray70]

Man I hate GFI and the new arc fault breakers here in Canada for residential. What a nuisance. Only thing more frustrating is the taper resistant plugs.

Im firm believer in making sure you have good ground, proper size normal breaker and wire, and call it a day. All this new stuff is garbage.

 

[SeymourDumore]

I'm repeating myself. I promise this is the last time I will say it. A GFCI breaker does not care whether "hot" wires are supply or neutral/return. It sums the current across all the hot wires, and trips if the sum is not (almost exactly) neutral. If you have 3-wire Delta service,

And I will repeat myself as well ....
Can you please show us a single device which will serve as a GFCI protection when the supply is a purely Delta service, let it be 240V or 480V?

Since 277/480V Wye for industrial is pretty much the standard, let's leave it alone.
So is 120/208V Wye in residential.

Instead, how about we focus on the 240V/Delta supply shall we?
I have a 4000A 240V Delta secondary transformer outside my shop.
There are only 3 sets of wires coming into my facility: L1-L2-L3, all of them are 240V L-L, no Ground or Neutral.
What exactly will the GFCI breaker would/should be referencing to?

 

[steve-l]

And I will repeat myself as well ....
Can you please show us a single device which will serve as a GFCI protection when the supply is a purely Delta service, let it be 240V or 480V?

Since 277/480V Wye for industrial is pretty much the standard, let's leave it alone.
So is 120/208V Wye in residential.

Instead, how about we focus on the 240V/Delta supply shall we?
I have a 4000A 240V Delta secondary transformer outside my shop.
There are only 3 sets of wires coming into my facility: L1-L2-L3, all of them are 240V L-L, no Ground or Neutral.
What exactly will the GFCI breaker would/should be referencing to?

Open the box where those wires go and look how they are connected. Educate yourself.

 

[gustafson]

Man I hate GFI and the new arc fault breakers here in Canada for residential. What a nuisance. Only thing more frustrating is the taper resistant plugs.

Im firm believer in making sure you have good ground, proper size normal breaker and wire, and call it a day. All this new stuff is garbage.

I have no problem with GFCI or AFCI breakers in my house. very very few nuisance trips

You kind of get used to the tamper resistant plugs but yeah, they are a pain

 

[SeymourDumore]

Open the box where those wires go and look how they are connected. Educate yourself.

OK, I am probably wording my posts incorrectly...
I understand the summing of the currents in all 3 legs, and Neutral is not needed to do that.
I absolutely agree there.
What I do NOT understand is how does a GFCI behave in a pure Delta service which can be either ungrounded, corner grounded or center-grounded?

 

[gustafson]

AFAIK no conductor called 'ground' should ever carry a current under normal circumstances,thus I would think how a circuit is grounded, or referenced to ground, is unimportant

 

[sfriedberg]

Yes, a GFCI breaker does not care which (if any) of the hot wires it is monitoring is grounded. It does not require a ground reference to operate, because it isn't really a "ground fault" detector. It is really a "unbalanced current" detector.

The most common way of getting unbalanced current on a circuit is through a ground fault. But that's not the only way. GFCI catches them all, regardless of specific cause.

 

[SeymourDumore]

The most common way of getting unbalanced current on a circuit is through a ground fault. But that's not the only way. GFCI catches them all, regardless of specific cause.

So what happens when your supply is a 240V ungrounded Delta?
A single line to ground short does not cause any current flow, therefore will go undetected.

 

[sfriedberg]

Yep. If your transformer and supply lines have perfect insulation, that short won't be detected, because no current is flowing. Effectively, no harm, no foul. If milliamp-level current ever flows along that path, the GFCI breaker pops.

US National Electric Code (NEC) does not require delta power to be grounded (in most cases). But there are a bunch of NEC Articles (250-5, 250-26, all of 250 part G) that are relevant to this scenario. The equipment bonding requirements in part G pretty much ensure that you're not going to be able to apply an AC potential to ground without generating some current. E.g., your whatever-to-Delta transformer output isn't required to be grounded, but the transformer case is required to be grounded. Figure the odds that you can short a transformer output to its case without having any impact on current flows.

[Added in edit] BTW, it would not be unusual for a 3-wire ungrounded Delta supply to have a grounding autotransformer added with a moderate value resistor between the autotransformer center tap and ground, exactly to provide a predictable return path for the ungrounded-delta-short-to-ground scenario to trip either normal overcurrent breakers or GFCI breakers. However, this is not, I think, a code requirement. (All I have at this location is an old, 1984 copy of the NEC Handbook; things may have changed in the last 38 years!)

 

[newtonsapple]

Ever since they changed the code to require that receptacles be installed upside down I concluded it was over run by busy bodies with nothing meaningful to occupy their lives. I know their "reason" but it's stupid!

Who decided they were the right way up in the first place?

The real silly part of NEMA 5-15 is they can easily expose a conductor prior to disconnecting. The ground pin on top reduces the risk of a direct short from something contacting exposed conductors. I've actually seen this happen twice related the fact that I work with with long straight wire like parts. Wire part rolls off the back of the bench or shelf along the wall. Being .060" OD by 3-4 feet long, turns out there are pretty good odds it can find its way to an exposed conductor on a plug that is slightly pulled out. It goes boom when it happens.

 

[SeymourDumore]

[Added in edit] BTW, it would not be unusual for a 3-wire ungrounded Delta supply to have a grounding autotransformer added with a moderate value resistor between the autotransformer center tap and ground, exactly to provide a predictable return path for the ungrounded-delta-short-to-ground scenario to trip either normal overcurrent breakers or GFCI breakers. However, this is not, I think, a code requirement. (All I have at this location is an old, 1984 copy of the NEC Handbook; things may have changed in the last 38 years!)

Yeah, I don't know what the POCO in this state is offering now for new industrial service.
My building was built in '79, initially supplied with a Wye service, but a few years later was changed to a 240 Ungrounded Delta due to load requirements. ( this is from the original owners )
Now, looking at the Eversource Energy ( our service provider ) webpage, 240V-Delta is no longer offered for new installations, only 120/208 or 277/480, both obviously Wye.
They also say that anyone needs 240V 3Ph service, or replace an existing 240V 3ph transformer must contact them for options.
I am guessing ( and just guessing here ) that they might provide an option to go with a non-standard transformer having a 240V-Wye secondary, where the center is grounded.
My service is 2000A from a pad mounted tranny, so I will find out what my options are when that sucker goes.