Changed Conditions and NEC article 250-140 and exceptions

[tortuga]

I have discussed it with the inspector. I have made corrections that they have required but i am appealing the decision to the county Electrical board of supervisors before i do anymore generator work in this particular county. They have interpreted this article WRONG. It is totally assinine for us as Electrical contractors to tell a customer

"Sure sir/mam, i can install your whole house generator BUT its gonna cost you an extra $1500 to $2,000.00 for me to re wire your existing 3 wire appliances to go along with it".

I agree with dennis you change a service to a sub you gotta figure modifications of the old service into your bid, floating neutral bar, separating grounds and neutrals and 3 wire cables.
Why would you re-run the circuit? You just need to meet code.
I think mbrooke's brilliant code interpretation would cost one role of super 88 white tape and about an hour of labor.
My solution get them a 4-wire and costs more, but not typically over $200, 1 scrap piece of #8 about 5 feet, one box, mudring, 14-40 and a split bolt.
In the photo I posted i was moving the range receptacle anyways and drwyaller took care of the patch for $50.

 

[Dennis Alwon]

See exception 3- insulated. Taping it makes it insulated.

You didn't read what I said. You are looking at the exception without IMO realizing it can't be used for this scenario... I know that NC made an exception for this section because of the issues with it.

This is what NC did about it

Exception No. 2: For existing branch-circuit installations only where an equipment grounding conductor is not present in the outlet or junction box, an equipment grounding conductor sized in accordance with 250.122 shall be permitted to be run separately from the circuit conductors.

This is saying that to avoid running a new cable they will allow an equipment grounding conductor to be run separately to the dryer or range outlet. That would be unnecessary if you didn't have to upgrade the branch cir., IMO.

 

[LarryFine]

Let's start with question #1:

Jslatt27, did you separate the grounds and neutrals in the panel?

 

[tortuga]

You didn't read what I said. You are looking at the exception without IMO realizing it can't be used for this scenario...

Are you saying that based on 250.140 Exception item (3)?
The OP would seem to meet all the criteria.
Seems like mbrook is reading it like you can be
Insulated
or
part of an SE cable and (the SE cable) originates at the service equipment.

I interpreted it like the neutral is either insulated 3 wire romex (like the pic I posted in post#14) OR SE cable with a bare neutral,
AND
Under either of those conditions they need to originate at the service equipment.
Thats why i do the 250.130(C) grounding.

 

[tortuga]

That NC Exception No. 2 is unnecessary?
as 250.130(C) already allows that no?

 

[LarryFine]

The ATS renders anything after it a feeder to a sub-panel.

 

[mbrooke]

You didn't read what I said. You are looking at the exception without IMO realizing it can't be used for this scenario... I know that NC made an exception for this section because of the issues with it.

This is what NC did about it



This is saying that to avoid running a new cable they will allow an equipment grounding conductor to be run separately to the dryer or range outlet. That would be unnecessary if you didn't have to upgrade the branch cir., IMO.

I can only imagine the reactance of that loop...

Any way, running a separate EGC would still require drilling and fishing to some degree.


IMO, wrapping it in tape makes it insulated even if thats not what the code intended.

 

[tortuga]

I can only imagine the reactance of that loop...

Any way, running a separate EGC would still require drilling and fishing to some degree.


IMO, wrapping it in tape makes it insulated even if thats not what the code intended.

Its a simple math problem;

A residential 200A service, say 50 kVA transformer available fault current 12550A.
#2AL triplex service drop say 50 feet in free air,
4/0 Al service entrance conductors say 20' on average in metallic conduit,
range wires #6 AL say 40 feet average.
Drop the EGC to code sizing #10 THHN say 50 feet.
Line to EGC fault inside the Range.
Inverse time breaker 40 amp
no motor contribution

Whats the trip time?

 

[mbrooke]

Its a simple math problem;

A residential 200A service, say 50 kVA transformer available fault current 12550A.
#2AL triplex service drop say 50 feet in free air,
4/0 Al service entrance conductors say 20' on average in metallic conduit,
range wires #6 AL say 40 feet average.
Drop the EGC to code sizing #10 THHN say 50 feet.
Line to EGC fault inside the Range.
Inverse time breaker 40 amp
no motor contribution

Whats the trip time?

Well, rather simple when Xl is listed in Chapter 9 Table 9, which assumes conductors next to each other. When separation is signficant resistance no longer dominates alone- from the IEEE Green Book:







Which in turn would technically (may) require a faster disconnection time-




Though in all fairness, the distances you list aren't to bad.

My point is that the OP taping up and grounding through the SE's concentric neutral is (IMO) superior to doing it any other way.

 

[tortuga]

I just figure the separation as infinite, plugged it into the bussman fault calculator and included the supplemental GEC as the last part of the 'run' and used a trip curve for a square d QO residential breaker, fault current was around 600-700 amps trip time .5 sec.
Your method fault current would be ~1600 amps so yeah faster trip time, i give you that .
allowing a N-frame bond at the range/oven introduces all kinds of other possibilities like neutral to gas pipe bond at the range/oven.
What would happen if the neutral opened between the generator and the subpanel?

I was more interested in your interpretation of the sentence in 250.140 Exception item (3).
I think Dennis and I interpret it like the range neutral has to be either:

• Insulated (as defined in art 100) AKA old 3 wire romex (like the pic I posted in post#14) OR
• SE cable with a bare neutral,

AND

• Under both of those conditions the neutral needs to originate at the service equipment for the exception to hold.

Now that the OP has changed a service to a sub he lost the exemption.

 

[mbrooke]

I just figure the separation as infinite, plugged it into the bussman fault calculator and included the supplemental GEC as the last part of the 'run' and used a trip curve for a square d QO residential breaker, fault current was around 600-700 amps trip time .5 sec.
Your method fault current would be ~1600 amps so yeah faster trip time, i give you that .
allowing a N-frame bond at the range/oven introduces all kinds of other possibilities like neutral to gas pipe bond at the range/oven.
What would happen if the neutral opened between the generator and the subpanel?

I was more interested in your interpretation of the sentence in 250.140 Exception item (3).
I think Dennis and I interpret it like the range neutral has to be either:

• Insulated (as defined in art 100) AKA old 3 wire romex (like the pic I posted in post#14) OR
• SE cable with a bare neutral,

AND

• Under both of those conditions the neutral needs to originate at the service equipment for the exception to hold.

Now that the OP has changed a service to a sub he lost the exemption.

Is the busman fault calculator assuming zero ohms or some type of impedance at the fault point? Just wondering.


I would agree that is the intent of the code, but at the same time the AHJ has discretion?

 

[tortuga]

Is the busman fault calculator assuming zero ohms or some type of impedance at the fault point? Just wondering.


I would agree that is the intent of the code, but at the same time the AHJ has discretion?

Here is a link to it:

Eaton's Bussmann Series - Available Fault Current Calculator

 

[LarryFine]

I was more interested in your interpretation of the sentence in 250.140 Exception item (3).
I think Dennis and I interpret it like the range neutral has to be either:

• Insulated (as defined in art 100) AKA old 3 wire romex (like the pic I posted in post#14) OR
• SE cable with a bare neutral,

AND

• Under both of those conditions the neutral needs to originate at the service equipment for the exception to hold.

Now that the OP has changed a service to a sub he lost the exemption.

I have been corrected here when I have said the service origination applies to both conditions; that it applies to only the latter.

I have asked for, and been given the okay to tape the bare SE conductor white when a new run would have been prohibitive.

In my opinion, the white tape is both insulative and indicative, and should be done carefully; half-lapping is adequate, IMHO.

 

[tortuga]

I have been corrected here when I have said the service origination applies to both conditions; that it applies to only the latter.

I have asked for, and been given the okay to tape the bare SE conductor white when a new run would have been prohibitive.

In my opinion, the white tape is both insulative and indicative, and should be done carefully; half-lapping is adequate, IMHO.

Those kind of sentences in the code remind me of 'diagramming' sentences in grade school LOL

So it just so happened that the touchpad in our range went bad, and to figure that out I had to get all into the range and how its wired internally.
The only thing connected to the neutral in our range is the oven light, a 40 watt bulb and , what appears to be a 120-24V transformer for the controls.
I am reminded what a waste of resources 4 wire ranges are.
I could literally put in a 240-24V transformer and a 240V bulb and have no need for a neutral.
I have no idea why manufacturers dont just do that then you could use a 6-50 and this kinda thing would not be an issue.

 

[mbrooke]

If one takes a look at 210.6 (A) I think we can again place blame on NFPA 70.