Serious error in MH Grounding vs Bonding Book?

[Skyline Electric]

Figure 250-160 is illustrating section 250.118(5) (Flexible Metal Conduit) and says:

"A bonding conductor is required when a circuit protection device exceeds 20A, or the fault current path of the conduit exceeds 6 ft"

However, in the actual NEC, 250.118(5) does not contain the word "or".

This illustration in the Grounding vs Bonding book indicates that FMC may be used as a EGC regardless of it's length as long as the OCPD is not over 20A.

Is the book in error? Is my interpretation of this section in error?

Thanks in advance. :-?

 

[mweaver]

Skyline,

...While I am unable to comment on Mr. Holt's book it appears your understanding may be correct...

The 2008 language in Section 250.118(5) for flexible metal conduit states that ALL the conditions must be met...

250.118(5) Listed flexible metal conduit meeting all the following conditions:
a. The conduit is terminated in listed fittings. -and-
b. The circuit conductors contained in the conduit ar protected by overcurrent devices rated at 20 amperes or less. -and-
c. The combined length of flexible metal conduit and flexible metallic tubing and liquidtight flexible metal conduit in the same ground return path does not exceed 1.8 m (6 ft). -and-
d. Where used to connect equipment where flexibility is necessary after installation, an equipment grounding conductor shall be installed.



(Mistakes are sometimes made in explanatory books. It is always important that you are also ALWAYS reading the source material to be sure that you do in fact understand what the source material is actually saying ...)

I hope this is helpful

mweaver

 

[Dennis Alwon]

Actually I think the wording is correct. Mike's statement is a reverse of art. 250.18(5), I think anyway. If the flex exceeds 6' or if the OCP is more than 20 amps a grounding conductor must be run

 

[Skyline Electric]

Actually I think the wording is correct. Mike's statement is a reverse of art. 250.18(5), I think anyway. If the flex exceeds 6' or if the OCP is more than 20 amps a grounding conductor must be run

I don't think the code supports that interpretation.

 

[Dennis Alwon]

I don't think the code supports that interpretation.

250.118(5) clearly states what must happen for flexible metal conduit to be used as an EGC. All of the conditions of (5) must be met.

Mike Holt states that if the flex exceeds 6' or if the OCPD is gretaer than 20 amps then the flex may not be used as a ground. It seems clear to me.

250.118 Types of Equipment Grounding Conductors.
The equipment grounding conductor run with or enclosing the circuit conductors shall be one or more or a combination of the following:

(5) Listed flexible metal conduit meeting all the following conditions:
a. The conduit is terminated in listed fittings.
b. The circuit conductors contained in the conduit are protected by overcurrent devices rated at 20 amperes or less.
c. The combined length of flexible metal conduit and flexible metallic tubing and liquidtight flexible metal conduit in the same ground return path does not exceed 1.8 m (6 ft).
d. Where used to connect equipment where flexibility is necessary after installation, an equipment grounding conductor shall be installed.

 

[Skyline Electric]

Ok Dennis, I misunderstood you, I thought you said "If the flex exceeds 6' or if the OCP is more than 20 amps a grounding conductor must be run" as if *that* was your position.

I agree that ALL the conditions must be met. I LOVE code discussions!

 

[Dennis Alwon]

Ok Dennis, I misunderstood you, I thought you said "If the flex exceeds 6' or if the OCP is more than 20 amps a grounding conductor must be run" as if *that* was your position.

I agree that ALL the conditions must be met. I LOVE code discussions!

I still think you are missing the point. I am saying if the flex is longer than 6' that an EGC must be used. I am also saying that if the OCPD is larger than 20 amps an EGC must be used-- the flex in both cases will not suffice as the EGC.

I agree all the condition must be met in order to use flex as an EGC -- that is the same as saying if any of the conditions are not met than an EGC must be run in the flex. Mike just used two of the conditions as an example.

I do not have his book but that is what it appears like to me.

 

[Skyline Electric]

If I had a 60' run of flex with 2 #14 THHN conductors protected with a 15 amp breaker, would I be required to pull a ground wire?

EDIT: OK Dennis, I think I finally get it! Obviously in this example I would need a ground wire!

 

[infinity]

If I had a 60' run of flex with 2 #14 THHN conductors protected with a 15 amp breaker, would I be required to pull a ground wire?

EDIT: OK Dennis, I think I finally get it! Obviously in this example I would need a ground wire!

It's more than 6' so yes.