Face down mounted receptacle - is there is weight rating?

[Jerry Peck - Codeman]

This question comes from a discussion I had with other inspectors.

Stated installation example: In a supermarket there is a ceiling mounted receptacle outlet in the acoustical tile ceiling which is used for seasonal refrigerated cases/coolers which are moved into place when desired. The connection is via a cord and plug to the receptacle outlet 14 feet above the floor.

There is no strain relief supporting the weight of the cord, the receptacle is supporting the weight of 14 feet that 20 foot long (cord length not measured, length is estimated based on ceiling height and cord laying on floor at cooler box) with the cord being 10-3 with ground SO cord.

Stated question is: *IS* a strain relief required to support the weight of that cord?

After looking through the 2008 NEC and the 2008 UL White Book and not finding anything allowing or limiting the weight on the receptacles, I sent an inquiry to UL for information and possibly an answer.

I will post that response when I receive it.

[Jerry Peck - Codeman]

The following is the reply I received back from UL.

Mr. Peck,

This email is a follow-up to our phone conversation based on the following question that I was forwarded from you;

I have been asked a question and am having a discussion regarding the following: Installation: A receptacle, duplex or single, is mounted face down in a ceiling mounted box. Condition: A cord and plug is plugged into the receptacle with the weight of the cord hanging down, pulling against the plug's prongs which in held in the receptacle by tension. Status: To date I have not found anything in the NEC or the UL White Book which allows for the above, nor have I found anything in NEC or the UL White Book which does not allow for the above. Position: Which position is defensible for a code official? - a) The installation is not allowed without the installation of a strain relief carrying the weight of the cord and plug. - b) The installation may be approved as installed. Information not provided: Length and weight of cord. Reason that information is not provided: There is nothing I have found which limits the weight or length of the cord. Additional query: I see nothing which allows for a twist-lock style receptacle and plug to be installed for this use either. What am I missing or not finding? Thank you, Jerry Peck Codeman http://www.AskCodeMan.com

It is stated by many who are responsible for interpreting the NEC that if not prohibited by the code then it is permitted. With that said, 110.3(B) requires listed or labeled equipment shall be installed and used in accordance with any instructions included in the listing or labeling.

The 08 NEC requires receptacles to be listed, 406.2. Also all attachment plugs, cord connectors and flanged surface devices are required by NEC 406.6 to be listed. The 08 UL White Book covers the typical attachment plug under category AXUT and receptacles under category RTRT. Both categories AXUT and RTRT use UL 498 as the UL Standard for evaluation.

UL 498 clause 87.1 requires a blade retention test so that the contacts of a 1-15R, 5-15R, 5-20R, 6-15R or 6-20R configuration cord connector shall retain an attachment plug so that a force greater than 3 lbf (13 N) is required to withdraw the plug when tested.

UL 498 clause 90.1.1 requires a second blade retention test for receptacles after completion of the Overload Test and the Temperature Test, the contacts of a 1-15R, 5-15R, 5-20R, 6-15R or 6-20R configuration cord connector shall retain an attachment plug so that when tested as described in this section:
a) A force greater than 3 lbf (13 N) is required to withdraw the plug, and
b) A force of 15 lbf (67 N) is capable of withdrawing the plug.

UL_blade_retention_01.jpg

These requirements apply to all general use receptacles, hospital and spec grade receptacles must comply with these requirements as well as additional blade retention tests. As for your question about twist lock type receptacles, by exemption in UL 498 they are not required to be tested for blade retention. Based on this information, I would surmise, that if the size and length of the cord exceed 3 pounds it is to heavy for the receptacle to adequately support it and the AHJ would be able to justify requiring strain relief for the additional cord weight.

UL_blade_retention_02.jpg

UL_blade_retention_03.jpg

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Thank you for contacting UL. If I can be of further assistance, please do not hesitate to contact me.

Jeffrey A. Fecteau C.B.O., E.C.O
Staff Engineer Associate

[Jerry Peck - Codeman]

The first example given in the original post WOULD require a strain relief of some type, either from the structure or from the ceiling grid, to which the weight of the cord could be supported, then swagged over to the receptacle, keeping the swagged cord short enough to keep the weight of the cord and plug to under the 3 pound limitation of the listed receptacle.

Another installation example of a receptacle outlet mounted face down in a ceiling would be for a garage door.

The cord for the garage door would weigh less than the 3 pounds in the listing test above, i.e., what the receptacle is tested and listed to support, this WOULD NOT require a strain relief to support the cord.

Regarding the twist lock type receptacles and plugs, twist-lock type receptacles are not required to have a blade retention test and therefore have no stated weight carrying ability. The twist lock feature is to avoid accidental disconnection of the plug from the receptacle. The twist-lock feature for retention is mechanical and not tension of the blade contacts. There is no weight rating test of the mechanical structure of the receptacle outlet to resist any weight, therefore there is no allowable weight rating for a twist-lock type receptacle.