grounding battery powered electronics in a plastic enclosure in Class I Div 2 locaton

[johnpbrewer]

Our product is battery powered, 7.2VDC, and contained in aplastic enclosure. We have options forsensor inputs and can provide 5V power to sensors. We are not sure of the grounding requirementsin both ordinary locations and hazardous locations.

Looking at the NEC in Article 250.160, our system will notrequire a ground since it is 2 wire DCand under 60V. However, we do haveprovision for a ground connection in our enclosure and would run a bondingjumper to that through a cable gland entry. We have some transient protection circuitry referenced to ground. I assume this will be OK. 250.102 (A) and 250.118 (1) both allow wireconductors.

For Class 1 Div 2 installations, however, the NEC states in501.30 that regardless of the voltage of the electrical system, wiring andequipment in Class I Division 1 and 2 locations shall be grounded as specifiedin Article 250 and in accordance with requirements of 501.30 (A) and (B).

Is a wire bonding jumper allowed per 501.30 (A)? Is conduit or flexible metal conduit required? 501.10 (B), Wiring Methods for Class I,division 2, does not list bondingjumpers. However, Exhibit 501.13 shows abonding jumper tied to flexible metal conduit to ensure effective connections, sincethe conduit is not considered a robust EGC in Class I Division 2. Since we have a plastic enclosure,only a bonding jumper through a cable gland will be used. Is thisacceptable?

 

[rbalex]

There are those that would say that the NEC only deals with installations. This is not entirely true with Classified locations. While it has been since the 2008 NEC that portable and mobile equipment were last addressed directly, there are still hints in Sections 501.130 and 501.140 and their analogs in Articles 502, 503 and 505 that at least some aspects of portable and mobile equipment are still concerns. Nevertheless, yours is a product standard issue.

That said, does your product have a NRTL certification such as CSA, FM, UL, etc.? There are multiple product safety standards that apply. Some, but not necessarily all, are listed in NEC Informative Annex A.

I must confess your plastic enclosure concerns me. It is not necessarily forbidden, but I would need far more detailed information about the product.

 

[johnpbrewer]

rbalex,

We are applying for CSA approval. This is where the issue arose. We have a ground/bond wire connected via a ring terminal to a mounting screw on our electronics board. We bring it out of the plastic housing through a cable gland. CSA has told us that the wire must conform to 501.10(B). However, single conductor ground wire (your typical 10AWG to 14AWG green jacketed copper cable) is not mentioned there. I believe that 501.10(B) wiring methods do not address ground/bond wire and that our wire type is OK to use. As i mentioned in the original post, Exhibit 501.13 shows a bonding wire tie strapped to some flexible conduit. It is the wire, not the conduit, that is providing the bond. So it appears that the ground/bond wire does not need to conform to the wiring methods of 501.10 (B).

We can connect a ground/bond wire in the method were are using. Correct?

The plastic enclosure has been accepted by CSA. There are no arcing or sparking components inside.

I don't believe that grounding/bonding is even required for this product. CSA agrees, as the product is being assessed without a ground connection. The ground/bond wire was removed from our product because of this issue.

However, some sensors that will be attached to our product require their chassis be connected to ground for approval purposes. Our product would be bonding to ground and we would pass this connection through one of the four wires in the cabling going to the sensor. The sensor has been designed for this. The sensor and cabling are approved for Class 1 Div 2 installations.

The other reason for the bond wire is for transient protection purposes. We clamp the remaining 3 lines (+V, return, signal) to the chassis ground in case of a surge on those lines.

Thank you for responding. I hope this addresses your questions.

 

[rbalex]

This is much better and CSA certification is fine as long as testing is to "Recognized [US] National Safety Standards".

NOTE: CSA is not automatically a NRTL unless testing is to "Recognized [US] National Safety Standards".

​

Grounding/Bonding is not a Section 501.10 issue; they are covered in Section 501.30. I also mentioned requirements for flexible cords are in Section 501.140. BTW these requirements are identical in virtually all Class I, II, and III and apply to both Divisions 1 & 2.

SO to address

Is a wire bonding jumper allowed per 501.30 (A)? Is conduit or flexible metal conduit required? ... Since we have a plastic enclosure,only a bonding jumper through a cable gland will be used. Is thisacceptable?

A wire bond is fine; in fact, it is a requirement in Section 501.140. No specific raceway is required.

 

[johnpbrewer]

Thank you for your responses.
Just to be certain, with a picture. This will be OK?

 

[rbalex]

I'm afraid that is still up to CSA to decide. While I can say it's my opinion that they seem to be misapplying Section 501.10(B), I'm not the one certifying the product.