IP Ratings - How many gland thread turns? 1

[KenAlmon]

I am aware of the IP ratings of electrical or instrumentation boxes. I am also aware that in order to maintain the rating, any gland entrances have to have a similar (or higher) rating. For example, a Hawke gland with an IP66 rating can be put in an IP66 box and the rating maintained. An IP66 gland in an IP67 box would only be an IP66 box when installed.

However, I am intrigued by several rumours going around our jobsite talking about the number of threads necessary to maintain ratings. There are several cases (perhaps more) to consider:

1. a clear hole in a box will require a metric (straight) gland with an IP washer (on the outside) and serrated washer (on the inside) and tightened to some tightness.
2. an NPT threaded (tapered) hub on the box will require a minimum of five (5) turns in order to maintain the IP rating. This may or may not be at the point where the gland is tight.
3. a metric threaded (straight) hub on the box will require a minimum of eight (8) turns in order to maintain the IP rating. There may or may not be an IP washer present.

My question is whether any of this is true and whether there is a basis such as a standard that specifically identifies the number of turns etc. It would seem to me that in the case of #1 above, you would have to have it some degree of tightness. In the case of #2, I would think you would have to have the gland tight, regardless of number of threads. And in the case of #3, I would think you would have to have an IP washer and it would have to be tight in the hub, again, regardless of the number of threads.

Perhaps the confusion relates to hazardous ratings where the Canadian Rules state:

Threaded joints that are required to be explosion proof or flameproof may be threaded either tapered or straight: where tapered must be 5 fully engaged threads and where straight, must be 8 fully engaged threads.

Although you would think the hazardous rating would at least equal IP rating...

Any ideas?

 

[busbar]

If ANSI standards are applicable, 1999 NEC 501-4.(a)(1) states: Threaded joints shall be made up with at least five threads fully engaged.

Additionally, the NPT thread taper is dictated in NEC 505-3.(b) All threaded conduit referred to herein shall be threaded with an NPT standard conduit cutting die that provides 3/4-in. taper per foot. Such conduit shall be made wrenchtight to prevent sparking when fault current flows through the conduit system, and to ensure the explosionproof or flameproof integrity of the conduit system where applicable.

Offhand, the range of cable sizes for the gland fitting would also be a factor. Too much slop would limit the minimum compression diameter, where too large a cable would not permit sufficient compressed surface area about the cable jacket.

 

[rossg]

Ken, I've just had to research this same matter myself, and referring to IEC standards I found the following:

IEC60079-1 (Flameproof 'd' equipment) Clause 5.3 and Tables 3 & 4 stipulate the minimum thread pitch and number of complete threads for both parallel and tapered screwed entries (five for both). This is to satisfy flame path length requirements, not IP rating. (I could find no stipulation in IEC60079-1 about any required IP rating, or maintenance of an enclosure's IP rating.)

IEC60079-7 (Increased safety 'e' equipment) Clause 4.9 (a) stipulates that an enclosure must have a minimum IP54 ingress rating (which means that a glanded entry must also be IP54 minimum). I could find no stipulation in IEC60079-7 as to the number of threads required to give the IP rating.

So for an Ex'e' enclosure, the number of threads is not the issue, but overall IP rating of the enclosure and entry is - use of the appropriate sealing washer with the gland will satisfy this, whether the entry is a clearance hole or a threaded entry.

For an Ex'd' enclosure, the number of threads on an entry is an issue, but this is related to flame path, not IP rating.