HRGU w/ Ground Fault Enabled on Breakers

[jim dungar]

The hazard does go down.

The hazard is the amount of Arc Flash Incident Energy (AFIE) typically expressed in cal/cm^2.
There is no industry consensus methodology, such as IEEE 1584, that calculates AFIE for anything except 3-phase (L-L-L) faults for 600V and less systems.

Yes, the first L-G fault on an HRG system is unlikely to result in a severe Arc Flash event. However, until the first fault is cleared, a second fault would be L-L which would likely propagate into a 3-phase event with the original AFIE level.

Reducing 'Risk' by lowering the probability of occurrence should be one of the goals of any Electrical Safe Work Practices program.

We need to use the definitions of the codes which which we are following.

 

[Sahib]

The hazard is the amount of Arc Flash Incident Energy (AFIE) typically expressed in cal/cm^2.There is no industry consensus methodology, such as IEEE 1584, that calculates AFIE for anything except 3-phase (L-L-L) faults for 600V and less systems. Yes, the first L-G fault on an HRG system is unlikely to result in a severe Arc Flash event. However, until the first fault is cleared, a second fault would be L-L which would likely propagate into a 3-phase event with the original AFIE level. Reducing 'Risk' by lowering the probability of occurrence should be one of the goals of any Electrical Safe Work Practices program. We need to use the definitions of the codes which which we are following.

1)The arc flash hazard due to lg fault can also be dangerous to life. By reducing lg arc flash hazard, HRG system also reduces risk of three arc flash hazard. 2)By code mandated detection of first gf which in op case by gf protection, risk of three phase arc flash hazard is also reduced in HRG system.

 

[jim dungar]

1)The arc flash hazard due to lg fault can also be dangerous to life.

In the US, we do not have an consensus standard that is used to calculate L-G arc fault hazard levels for 600V and less.
The highest AF incident energy hazard will be for a 3-phase fault. The highest hazard is not reduced when using HRG. Have you read IEEE1584 to see how grounding is considered when analyzing arc faults in order to determine incident energy?

 

[Sahib]

Section 7.2.2 of IEEE Red book states that when using HRG, there is no arc flash hazard as there is with solidly grounded systems since the fault current is limited to about 5A. The Red book refers to lg fault here.

 

[jim dungar]

Section 7.2.2 of IEEE Red book states that when using HRG, there is no arc flash hazard as there is with solidly grounded systems since the fault current is limited to about 5A. The Red book refers to lg fault here.

You need to get of your school books.

The 'red book' is seriously out of date in regards to many industrial practices and products, when was it last published? Until the L-G fault is cleared a second fault could be L-L-G which is not mitigated by the HRG.
Since 2004, IEEE1584 is one of the consensus standards used to determine the Incident Energy in an arcing fault situation. This calculated value is used to choose PPE for people that may be exposed to the arcing fault. The worst case IE is not mitigated by an HRG.

 

[Ingenieur]

You need to get of your school books.

The 'red book' is seriously out of date in regards to many industrial practices and products, when was it last published? Until the L-G fault is cleared a second fault could be L-L-G which is not mitigated by the HRG.
Since 2004, IEEE1584 is one of the consensus standards used to determine the Incident Energy in an arcing fault situation. This calculated value is used to choose PPE for people that may be exposed to the arcing fault. The worst case IE is not mitigated by an HRG.

a 5 A l-g fault is unlikely to migrate to l-l
it is no different than a 1.4 kw single ph load
Granted, if you crush a cable/conduit you'll likely get both

your point is that the hazard is based on the worst case scenario l-l
and the probability of this occuring remains the same since ngr does nothing (could be argued a little since it eliminates l-g that may develop into l-l) to mitigate
accepted as fact

but in reality it does improve safety
removes the largest fault type from the set of possibilities or at least reduces them to a non-dangerous level

 

[jim dungar]

a 5 A l-g fault is unlikely to migrate to l-l
it is no different than a 1.4 kw single ph load
Granted, if you crush a cable/conduit you'll likely get both

your point is that the hazard is based on the worst case scenario l-l
and the probability of this occuring remains the same since ngr does nothing (could be argued a little since it eliminates l-g that may develop into l-l) to mitigate
accepted as fact

but in reality it does improve safety
removes the largest fault type from the set of possibilities or at least reduces them to a non-dangerous level

I never said an HRG does not improve safety. It absolutely lowers risk of a fault.

While a L-G fault is not likely to 'grow' into a L-L fault, there is the situation where the company does not clear the L-G fault in a timely manner, because they can keep running, and then a second independent fault occurs.

 

[Ingenieur]

I never said an HRG does not improve safety. It absolutely lowers risk of a fault.

While a L-G fault is not likely to 'grow' into a L-L fault, there is the situation where the company does not clear the L-G fault in a timely manner, because they can keep running, and then a second independent fault occurs.

Not a fan of ngr without tripping or at least annoying non-clearing alarming
in my field it trips with 3 levels of sensing and 2 of interruption

 

[Sahib]

In OP case, gf detection is by tripping the system. And that anwsers OP's query.

 

[Sahib]

So why they need HRGU system then, they can get just the regular GF protection on breakers?

The GF protectin on breaker may trip on existing leakage current in the system. But it may be used with HRG without lowering its sensitivity very much (NGR may also lower existing leakage current in the system!).