Raco 943 4-Gang Box
During a new construction installation where one of our rough-in crews was installing a four-gang steel box in multiple patient care rooms for 277 volt lighting, the electrician who was the crew lead brought-up the fact that he believed that any circuit over 250 volts to ground required a bond bushing to bond the EMT or HCF armored cable to the box. This was the beginning of an enjoyable learning experience.
Here are the players:
Location:
- Patient Care & ICU rooms in a hospital
Parts:
- HCF AC as a wiring method
- EMT as a wiring method
- RACO 943 4-gang steel box
- 277 volt lighting circuits
References:
- 2008 NEC
- UL White Book
People:
- The crew lead
- The project foreman
- Head of the electrical department of Red Rocks Community College
- Me
The crew lead and I have known each other since nearly the beginning of my electrical career, and although I was working on a different project on the same job site, he knows that I enjoy electrical code. When he shared the situation with me, the first thing we did was look in the 2008 NEC. We found code article 250.97 which states:
For circuits of over 250 volts to ground, the electrical continuity of metal raceways and cables with metal sheaths that contain any conductor other than service conductors shall be ensured by one or more of the methods specified for services in 250.92(B), except for (B)(1).1
There is also an exception which follows 250.97, which basically states that if oversized, concentric, or eccentric knockouts are not encountered, or if they are encountered and the box is listed to have reliable bonding, then one of four methods in a list which follows can be used to connect the wiring method to the box. These methods are fairly standard, such as AC connectors and EMT connectors that have a lock nut on the inside of the box. From this, we knew that we had to find out if this box was listed for the exception, otherwise we would have to purchase bond bushings or use one of the other approved methods to ensure bonding.
Later that night at school (Red Rocks Community College), I told the head of the electrical department about our situation. He asked me if I knew why the box did not need bond bushings. When I said that I did not, he took me to a case of 4 square Raco boxes and showed me the label:
Click for larger image.
From this, these boxes were most likely listed for the exception due to the notice on the labeling, although I had not yet verified the listing.
When I arrived at work the next day, I showed the crew lead the label on a case of 4 square boxes that we had on our parts shelves which were close to our morning meeting spot. The next step was to verify that the label on the 4 gang case was the same as the label on the 4 square case. We walked upstairs after our morning meeting and went straight for the case of 4 gang boxes. We looked at the label, and to our disappointment, the space where the notice should have been on the label was blank. Our only option now was to turn to the UL White Book and check the listing, which I planned to do that night when I got home.
The project foreman beat me to it and I will share the process he used to find the answer. First, we want to access Raco’s website. We then want to look-up the 4 gang box which we were using, the Raco 943. On the page for the Raco 943, at the bottom, it shows the compliances: UL 514-A, File E195978. UL 514-A is the UL Standard for Metallic Outlet Boxes, and is a bit of a boring read even for me, which is fine because we do not need access to this document to find our answer (a manufacturer would find the information vital, however). It is time to turn to the UL website and it’s search function.
On the UL website, we can find a page that shows us the UL White Book category for our box and a list of all Raco products which are listed under that category. Using the file number E195978, we see that this file and therefore our box is attached to the QCIT category in the UL White Book, and on the same page we can also find our box’s product number under the Outlet boxes group: “941-945 incl.,” which means our Raco 943 definitely falls under QCIT. Going to the UL White Book, we can look at the QCIT category which is for Metallic Outlet Boxes [Outlet Boxes and Fittings]. Under QCIT, we find the following information:
CONCENTRIC OR ECCENTRIC KNOCKOUTS
All boxes with concentric or eccentric knockouts have been investigated for bonding and are suitable for bonding without any additional bonding means around concentric (or eccentric) knockouts where used in circuits above or below 250 V, and may be marked as such.2
Now we had our answer. The boxes did not require additional bonding.
This situation was a good example of an instance where the NEC did not have the complete answer. The UL White Book is another source with which an electrician should be familiar. Although UL’s website can take some practice to use, once the search function is mastered, all one has to do is either know the file number or the White Book category and they can usually find the answer when a question of listing arises.
Since we are on the topic of UL’s website, I will share with you the UL code correlation database which is also found on UL’s site. Using it, one can enter the code document, for example NEC 2008, and then the code article itself, 250.97, and then search. In the list produced from the database, I can see the QCIT category. One can also search by UL category and obtain a list of NEC code articles that relate to the category. Enjoy!
