Why more relaxed equipment grounding rules for DC?

[unsaint34]

250.112 (A) states I don't have to equipment ground the frames of 2-wire dc switchboards where effectively insulated from ground.

250.134
Exception No. 2: For dc circuits, the equipment grounding conductor shall be permitted to be run separately from the circuit conductors.

I always thought DC was more dangerous than AC, which would make more sense to follow equipment grounding more strictly when dealing with DC. Why does NEC take such latitude with DC?

Thanks in advance.

 

[iwire]

250.112 (A) states I don't have to equipment ground the frames of 2-wire dc switchboards where effectively insulated from ground.

That is really not that much different than what 250.110 says for AC but in a different way.

250.134
Exception No. 2: For dc circuits, the equipment grounding conductor shall be permitted to be run separately from the circuit conductors.

I believe the deal here is that with DC circuits an EGC run separately is just as effective as an EGC run with the circuit.

On the other hand with AC circuits an EGC run separately is less effective, I think this is due to impedance only found on AC circuits.

I always thought DC was more dangerous than AC, which would make more sense to follow equipment grounding more strictly when dealing with DC.

I think that is more of an old wives tail than reality.

Why does NEC take such latitude with DC?

I do not think it is.

The above are just my opinions, I could well be wrong.

 

[RB1]

Inductive reactance is not an issue with steady-state DC. The proximity of the return path to the source doesn't affect the resistance of the circuit.

 

[unsaint34]

That is really not that much different than what 250.110 says for AC but in a different way.

Would you care to explain further? I think you are referring to 250.110's exception #1 & 3, which allow no equipment grounding if the mentioned equipment were double (or effectively) insulated. However, 250.112 specifically talks about the 2wire DC switchboards. So, there must be some special quality about 2wire DC switchboard that exempts the EG rule. I am thinking something to do with capacitance and induction?

 

[unsaint34]

I believe the deal here is that with DC circuits an EGC run separately is just as effective as an EGC run with the circuit.
On the other hand with AC circuits an EGC run separately is less effective, I think this is due to impedance only found on AC circuits.

I initially thought about the inductive reactance; and the dangerous heating effect of separating paralleled circuit conductors by phases. Then I thought that shouldn't be an issue since EGC is normally a non-current carrying conductor. But I guess there are situations where current can continously flow through the EGC without being detected, such as ground fault of grounded conductor.