Ground. Fault Protection

[Sajid khan]

Why Ground fault protection is not a mandatory requirement like Overload, short circuit and instantaneous protection.
As per NEC rule breaker of 1000A or greater shall have ground fault protection.
Thanks


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[winnie]

All protective devices cost money, use energy, and have undesired consequences such as 'nuisance tripping'.

Writing code requirements is a rather political process, but I assume that the code panel decided that Ground Fault protection on services smaller than a certain size did not provide sufficient benefit to be worth the additional cost.

-Jon

 

[Jraef]

All protective devices cost money, use energy, and have undesired consequences such as 'nuisance tripping'.

Writing code requirements is a rather political process, but I assume that the code panel decided that Ground Fault protection on services smaller than a certain size did not provide sufficient benefit to be worth the additional cost.

-Jon

As evidenced by the fact that prior codes did not require GFEP at all... I don't remember when that happened though. The oldest NEC I have now is 2002, it was required then, but I don't think it was there in 1978 because I remember installing switchboards that didn't have it back then. I could be wrong about that though, I was a pup back then.

 

[paulengr]

Why Ground fault protection is not a mandatory requirement like Overload, short circuit and instantaneous protection.
As per NEC rule breaker of 1000A or greater shall have ground fault protection.
Thanks


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To put it politely, grounding is one of the most pervasive and least understood parts of the electrical system. To put something in the Code you have to among other things show a need for it these days. Some sort of documentation of the risk. And show that it’s feasible. Also although it is quickly getting away from this, electricians are supposed to follow Code. If it turns into an engineering project there better be a very good reason. The one line arc flash rule is still a huge issue and the SCCR rules aren’t much better.

Most of the time on smaller loads for instance phase overcurrent does double duty. And if we introduce it, pray tell how are you going to do coordination? And how to check coordination between the two? Without a $10,000 software program and a $5,000 engineering study for every house built? And if so, what’s the risk? That’s why the rule for roughly 1,000 A and over is totally inadequate, totally arbitrary, and nowhere near what it should be but so far nobody has yet come up with a better one. This rule has changed multiple times and nobody is happy with it but there have been no better ideas put forward. In engineering circles they promote the idea of using EMTP for everything! That’s overkill even for engineers.

 

[rnatalie]

GFCI requirements were added to the NEC in 1978. Pricey back then, you typically had one GFCI serving all the protected receptacles. The requirement has expanded over the year.

Such is not uncommon with things in general. AFCI's started with just bedroom outlets but were expanded to things over the next couple of code cycles. Not only was price an issue, but it took the emergence of dual-AFCI/GFCI to make that practical across the board.

Even the requirement for equipment grounds has evolved over time.

 

[Sajid khan]

To put it politely, grounding is one of the most pervasive and least understood parts of the electrical system. To put something in the Code you have to among other things show a need for it these days. Some sort of documentation of the risk. And show that it’s feasible. Also although it is quickly getting away from this, electricians are supposed to follow Code. If it turns into an engineering project there better be a very good reason. The one line arc flash rule is still a huge issue and the SCCR rules aren’t much better.

Most of the time on smaller loads for instance phase overcurrent does double duty. And if we introduce it, pray tell how are you going to do coordination? And how to check coordination between the two? Without a $10,000 software program and a $5,000 engineering study for every house built? And if so, what’s the risk? That’s why the rule for roughly 1,000 A and over is totally inadequate, totally arbitrary, and nowhere near what it should be but so far nobody has yet come up with a better one. This rule has changed multiple times and nobody is happy with it but there have been no better ideas put forward. In engineering circles they promote the idea of using EMTP for everything! That’s overkill even for engineers.

Yes absolutely agree.. Requirement of ground fault for 1000A or Above doesn't mean that the ground fault cannot happen below 1000A. It can happen any where in the system.So why no ground fault below 1000A is not understandable..


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[winnie]

Remember that ground fault protection for 480V 1000A and above services is a rather different beast than GFCI protection.

In 480/277V services, an arcing ground fault can be sustained, meaning that once the arc is formed it does not self extinguish. This arc will produce a large amount of heat. However because it is not a solid bolted fault the current is somewhat limited.

My understanding is that the arc can limit current such that a large (1000A and above) OCPD might not open in the event of an arcing ground fault, but a smaller device would likely open because of the arc overcurrent. In other words, because the arc limits current, large OCPD does not provide protection from arcing ground faults, but small OCPD does. This is the issue that the ground fault protection requirement was intended to solve.

If the existing OCPD is sufficient to provide protection for arcing ground faults, why add the expense of ground fault protection?

I am not saying that ground fault protection is of no value on smaller services, simply that the benefit is smaller and must be weighed against the cost.

-Jon

 

[brantmacga]

GFCI requirements were added to the NEC in 1978. Pricey back then, you typically had one GFCI serving all the protected receptacles.

I was told by many the SOP back then was to move the one GFCI from house to house after each inspection. I know some guys were caught doing it here when AFCI’s came out too.


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[paulengr]

Yes absolutely agree.. Requirement of ground fault for 1000A or Above doesn't mean that the ground fault cannot happen below 1000A. It can happen any where in the system.So why no ground fault below 1000A is not understandable..


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As I said that is the issue. On small systems all fault currents exceed overcurrent protection so ground fault protection is automatic. And this is different from differential sensitive earth fault protection to use a more generic term than GFCI which is sometimes not appropriate anyway (nuisance trips on power converters that naturally have common mode currents).

So how do we create a rule requiring ground fault protection that captures everything without implementation issues? If you know, by all means submit a public input.

 

[paulengr]

Remember that ground fault protection for 480V 1000A and above services is a rather different beast than GFCI protection.

In 480/277V services, an arcing ground fault can be sustained, meaning that once the arc is formed it does not self extinguish. This arc will produce a large amount of heat. However because it is not a solid bolted fault the current is somewhat limited.

This case rapidly (within 1 cycle) turns into a three phase arcing fault, no ground needed. The latest IEEE 1584 update recognizes they are identical even in ungrounded systems.

My understanding is that the arc can limit current such that a large (1000A and above) OCPD might not open in the event of an arcing ground fault, but a smaller device would likely open because of the arc overcurrent. In other words, because the arc limits current, large OCPD does not provide protection from arcing ground faults, but small OCPD does. This is the issue that the ground fault protection requirement was intended to solve.

See above. The issue is that bolted ground faults may not trip short circuit protection or not very quickly. Nothing at all to do with arcing faults.

If the existing OCPD is sufficient to provide protection for arcing ground faults, why add the expense of ground fault protection?

I am not saying that ground fault protection is of no value on smaller services, simply that the benefit is smaller and must be weighed against the cost.

-Jon

Depending on the bonding the fault path can have a higher impedance and persistent energized metal parts that are normally grounded can exist. Plus the ground path may not take the expected route. That’s the concern.