What code section do you find absolutely ridiculous?

[Strathead]

Oh yeah that reminds me of two more in the exact same vein. If I parallel conductors the ground in each conduit has to be sized per 250.122 but if I don't put a ground in at all because I am using metal pipe that is fine. Same thing with your situation. If I put a ground in the 20 conduit with #6 then #6, don't .put a ground in at all, then OK.


The parallel thing really irks me. We absolutely should be able to provide grounds sized to account for parallel paths.

 

[iceworm]

I am the alternate to Robert Kauer on CMP 10. We both had the same issue and that is why we wrote that explanation.

I am working to fix this issue for the 2017 code.

Chris

Most any place the code says "or approved eqivalent", is screwed up - 240.87 is a good example.

Will all the inspectors that understand IEEE 1584 please raise their hand. Hummm - out of 10,000 inspectors, seven raised their hand.

Okay - of you seven, how many will spend the time to verify a solution is equivalent? Okay one left.

And since it has to be an "approved" equivalent, what is your plan if the design engineer did not meet your design preference? Interesting - now designs are based on the phase of the moon, or perhaps which side of the bed the inspector got up on

This is not a slam on inspectors - it is a comment on training, expertice, and funding.

How to fix? Well, if CP 10 wants to move the NEC farther into being a design guide - do nothing. The section becomes just another design mandate to get around by throwing money at it. Near as I can tell - all one has to do is pick a CB where the Instaneous can be set up out of the way if needed. Perfectly useless, meets code, costs money

If the code panel goal is reduction of arc-flash to where an incident is survivalable - then say so. Whoops - can't do that. Even with the instantaneous set, some lineups have in excess of 40cal/cm^2

No, this is in there because some other code panel (or was that under CP10 as well) demanded coordination. Some AHJ interpret as requiring coordiination to zero time. The only way to do that is to ditch the instantaneous. CP10 is putting a bandaid on an infected toe.

Or, CP 10 could change to "designed under engineering supervision". "approved equivalent" is useless throw away language - it means NO - use one of the following three because the AHJ has neither the time, inclination, or training to "approve" any other design.

Yes, it is an example of poor code - You (plural) are writing a design guide.

ice

 

[bob]

I understand and agree with the reasoning for that section that requires that, but think your example is a kind of side effect not taken into consideration when writing that section, yet they have had a chance to correct it but have not done so.

I think that requirement is the most ridiculous rule in the book. No technical reason for this requirement.

 

[Strathead]

I'm proud of myself. This is a great thread! I know there are many great minds here who contribute to code writing and are very involved. Hopefully some of this will trickle down to them and some discussion can take place to correct some issues. I have to say, up to this point the EGC size issues are the best place to start!

 

[raider1]

Most any place the code says "or approved eqivalent", is screwed up - 240.87 is a good example.

Will all the inspectors that understand IEEE 1584 please raise their hand. Hummm - out of 10,000 inspectors, seven raised their hand.

Okay - of you seven, how many will spend the time to verify a solution is equivalent? Okay one left.

And since it has to be an "approved" equivalent, what is your plan if the design engineer did not meet your design preference? Interesting - now designs are based on the phase of the moon, or perhaps which side of the bed the inspector got up on

This is not a slam on inspectors - it is a comment on training, expertice, and funding.

How to fix? Well, if CP 10 wants to move the NEC farther into being a design guide - do nothing. The section becomes just another design mandate to get around by throwing money at it. Near as I can tell - all one has to do is pick a CB where the Instaneous can be set up out of the way if needed. Perfectly useless, meets code, costs money

If the code panel goal is reduction of arc-flash to where an incident is survivalable - then say so. Whoops - can't do that. Even with the instantaneous set, some lineups have in excess of 40cal/cm^2

No, this is in there because some other code panel (or was that under CP10 as well) demanded coordination. Some AHJ interpret as requiring coordiination to zero time. The only way to do that is to ditch the instantaneous. CP10 is putting a bandaid on an infected toe.

Or, CP 10 could change to "designed under engineering supervision". "approved equivalent" is useless throw away language - it means NO - use one of the following three because the AHJ has neither the time, inclination, or training to "approve" any other design.

Yes, it is an example of poor code - You (plural) are writing a design guide.

ice

The intent of 240.87 is to provide additional means to reduce arc energy when a circuit breaker is used with out an instantaneous trip function engaged.

As you have pointed out the reason for the removal of the instantaneous trip function is most commonly done to accommodate selective coordination. Many large industrial facilities will try to achieve selective coordination to try to limit uncontrolled outages and cascading of overcurrent protective devices.

The mistake that was made during the last NEC revision cycle is that the whole purpose was lost with the revisions and if you read the section in the code today it applies to all 1200 ampere circuit breakers not just those with the instantaneous trip function disengaged.

For the 2017 NEC i am working on getting an instantaneous trip function put back into the code section to clearly indicate that the other methods to reduce arc energy are only required when a circuit breaker is used without an instantaneous trip function engaged.

Chris

 

[jim dungar]

The mistake that was made during the last NEC revision cycle is that the whole purpose was lost with the revisions...

This looks like another case where it is better to start over, rather than twist the existing language. It is too bad, most CMP's do not seem to understand this concept.

It seems that every cycle we go end up with unintended consequences, because of typos like poor punctuation. Then when it is time to fix it, nobody want to get rid of what was there, because it has become 'tradition'.

 

[iceworm]

Absolutely the panel was trying to do the right thing - no question in my mind on that issue. I am always impressed by all code panel members. I couldn't do it - for a whole bunch of reasons.

... As you have pointed out the reason for the removal of the instantaneous trip function is most commonly done to accommodate selective coordination. Many large industrial facilities will try to achieve selective coordination to try to limit uncontrolled outages and cascading of overcurrent protective devices. ...

Absolutely - but don't leave out the poorly worded, code mandated, coordination, down to zero time (gag) . Be that as it may, lets look at some physics about what you just said.

First look at the incident energy on a 13.8kV/480V, 1000kVA, secondary. Normal design primary CB have an instantaneous setting. Incident energy is well above 40cal/cm^2. No fix for this.

Now look at the load side of the secondary CB of a 2.5MVA, 5.5%, 480V, ASCC ~ 55KA. With the instantaneous in, again the energy is >40cal/cm^2. But the worst is likely in the short-time region - say 80%. 240.87 doesn't do anything to fix that - cause we got an instantaneous.

The only place this section might do some good is in the range of 1000A - 2000A. Outside of that range, it doesn't help, it just spends money.

The intent of 240.87 is to provide additional means to reduce arc energy when a circuit breaker is used with out an instantaneous trip function engaged. ...

If the CP is trying to say they want fuses above 1200A - then say so.

... For the 2017 NEC i am working on getting an instantaneous trip function put back into the code section to clearly indicate that the other methods to reduce arc energy are only required when a circuit breaker is used without an instantaneous trip function engaged. ...

My translation is way different. Here is where I think CP10 is going:

The NEC is moving farther into design guide status. 1200A and up shall have a maintenance switch to set the short-time to no intentional delay. 2000A and up shall have differential relaying or zone-selective interlocking. Relaying/interlocking shall operate per-unit across transformers.​

Either way, get rid on that damned "approved equivalent". Either specify exactly the methods to be used, or allow "under engineering supervision".

Or, there is one other: For other than cookie cutter installs - get out of the design business.

just personal thoughts - nothing I would ever consider or recommend to be binding.

ice

 

[Pharon]

This looks like another case where it is better to start over, rather than twist the existing language. It is too bad, most CMP's do not seem to understand this concept.

It seems that every cycle we go end up with unintended consequences, because of typos like poor punctuation. Then when it is time to fix it, nobody want to get rid of what was there, because it has become 'tradition'.

Couldn't agree more. Get rid of the selective coordination requirement - as it's a design issue, not a safety issue - and there will be no need for 240.87.

 

[Maders]

The intent of 240.87 is to provide additional means to reduce arc energy when a circuit breaker is used with out an instantaneous trip function engaged.

And this 'means' is now mandated on all systems - regardless of initial incident energy or the reduction of arc energy introduced by said means. In other words, the mandate is to include these systems regardless of their need or effectiveness.

This requirement feels more like a restraint of trade being promoted by certain manufacturers rather than addressing a serious safety concern.

 

[kwired]

Oh yeah that reminds me of two more in the exact same vein. If I parallel conductors the ground in each conduit has to be sized per 250.122 but if I don't put a ground in at all because I am using metal pipe that is fine. Same thing with your situation. If I put a ground in the 20 conduit with #6 then #6, don't .put a ground in at all, then OK.


The parallel thing really irks me. We absolutely should be able to provide grounds sized to account for parallel paths.

If you parallel conductors in separate raceways the main idea of a 250.122 full sized EGC in each raceway instead of reduced EGC's in each is if there should be a fault in one of the raceways the EGC in that individual raceway needs to carry the necessary current to allow the overcurrent device to open.

What if you paralleled four 200 amp conductors to get an 800 amp circuit, but only placed the typical 6AWG EGC that would be used for a 200 amp circuit in each raceway? Then if you had a phase to ground fault in one of the raceways that 6 AWG EGC is all that is there to clear an 800 amp overcurrent device. It may still do it but because it has more resistance then the 1/0 required for an 800 amp device and will take more time to meet the trip curve of the device.

I know that using four sets of parallels for 800 amps isn't all that common but isn't illegal either.

 

[Strathead]

If you parallel conductors in separate raceways the main idea of a 250.122 full sized EGC in each raceway instead of reduced EGC's in each is if there should be a fault in one of the raceways the EGC in that individual raceway needs to carry the necessary current to allow the overcurrent device to open.

What if you paralleled four 200 amp conductors to get an 800 amp circuit, but only placed the typical 6AWG EGC that would be used for a 200 amp circuit in each raceway? Then if you had a phase to ground fault in one of the raceways that 6 AWG EGC is all that is there to clear an 800 amp overcurrent device. It may still do it but because it has more resistance then the 1/0 required for an 800 amp device and will take more time to meet the trip curve of the device.

I know that using four sets of parallels for 800 amps isn't all that common but isn't illegal either.

I don't possess the design knowledge and mathematics necessary to factually compute, but I totally disagree with you for several reasons. First, I don't have to put a ground in at all and the steel of the 2" EMT is enough to satisfy code. Second, if you have a fault in one of the raceways in your scenario and it is non metallic then the fault is still fully capable and likely to take multiple paths back to the source and clear the fault, including and especially the other parallel ground wires in the other conduits. It is considered safe enough for multiple constant current paths then it whould be safe enough to consider multiple ground paths.

 

[kwired]

I don't possess the design knowledge and mathematics necessary to factually compute, but I totally disagree with you for several reasons. First, I don't have to put a ground in at all and the steel of the 2" EMT is enough to satisfy code. Second, if you have a fault in one of the raceways in your scenario and it is non metallic then the fault is still fully capable and likely to take multiple paths back to the source and clear the fault, including and especially the other parallel ground wires in the other conduits. It is considered safe enough for multiple constant current paths then it whould be safe enough to consider multiple ground paths.

If the fault occurs in the non metallic conduit other paths do not come into play until current has first passed through the EGC for whatever distance it is to a connection point to these other pathways. I also understand you don't need a "wire" EGC in a metal raceway but if you should choose to put one in anyway it must meet the same size rules as does an EGC in a non metallic raceway. If you want that changed you are free to submit a proposal, but it has been the way it is for a very long time and I think you would need to provide a lot of technical details maybe even some true testing data before it would even have a chance to get very far in the process.

 

[don_resqcapt19]

I think most here agree but, without an exception to the rule it is what it is.

Roger

They could make this problem go away by making T250.122 work like T250.66. If you base the EGC size on the size of the ungrounded conductors, there is no need for any calculations or adjustments where larger than normal conductors are used. You would just look up the ungrounded conductor size and read across the table to find the EGC size.

 

[don_resqcapt19]

Couldn't agree more. Get rid of the selective coordination requirement - as it's a design issue, not a safety issue - and there will be no need for 240.87.

There would still be a need for 240.87... most selective coordination is based on design requirements, not code requirements. Selective coordination increases the incident energy, triggering the need for 240.87.

 

[don_resqcapt19]

I'm proud of myself. This is a great thread! I know there are many great minds here who contribute to code writing and are very involved. Hopefully some of this will trickle down to them and some discussion can take place to correct some issues. I have to say, up to this point the EGC size issues are the best place to start!

So I can assume we will see some "public inputs", formerly known as proposals, from you for the 2017 code.

 

[kwired]

They could make this problem go away by making T250.122 work like T250.66. If you base the EGC size on the size of the ungrounded conductors, there is no need for any calculations or adjustments where larger than normal conductors are used. You would just look up the ungrounded conductor size and read across the table to find the EGC size.

I like that idea, even for motor applications where you often have overcurrent devices that are higher setting then conductor ampacity, I think it makes more sense to go by ungrounded conductor size instead of overcurrent device setting.

 

[Strathead]

So I can assume we will see some "public inputs", formerly known as proposals, from you for the 2017 code.

Not sure, I am smart enough to see things that bother me, but compared to some of you here, I feel quite dumb!

 

[kwired]

Not sure, I am smart enough to see things that bother me, but compared to some of you here, I feel quite dumb!

Making a proposal is not for everyone, you will need to provide good enough information to convince the CMP a change is necessary, and before you even get that far you really need to understand why a particular section is written the way it is, because your concern may have been addressed before but may have had other complications keeping it from advancing, find the right reasons to convince the CMP (just a slight variation of wording could be all it takes or some good research data on a topic) and it just may be accepted.

Posting your opinion here still doesn't hurt as there are people here that submit proposals as well as some that are on some CMP's and they will take this information into consideration if you have valid points and not just a complaint of "why do I have to do this".

 

[hornetd]

Dumbing down installations

Dumbing down installations

200.7(C)(1).

Having to remark a white that's used for an ungrounded in a switch loop is silly. If you pull out a switch and it has a black and white from an NM cable on it, and you can't figure out the white is hot, you don't need to be messing with it.

I see that as dumbing down installations in order to protect unqualified persons from the hazards of performing their own work.

 

[hornetd]

Uh Oh Don's talking sence again

Uh Oh Don's talking sence again

All rules that cover things beyond the outlet should be removed from the code. Those rules belong in the product standards, not in an electrical installation standard.

Don

If you keep making sensible proposals about the NEC there is an increased risk that it will begin to make sense. That, Sir, will upset the entire balance of the universe.