Motor fuel dispensing facilities

[bnd]

Article 514.9/A A listed seal shall be provided in each conduit run entering or leaving a dispenser or any cavities or enclosures in direct communications therewith. The sealing fitting shall be the first fitting after the conduit emerges from the earth or concrete.
Then theres 505.16/A-2 Explosionproof Equipment.
Conduit seals shall be provided for each conduit entering explosionproof equipment where there are splices etc.
? Are we trying to keep the vapor out of the dispenser J box where the splices are ( 505.16 )or we trying to keep the vapor from leaving the containment below the dispenser ( 514.9 ).
BND

 

[don_resqcapt19]

Re: Motor fuel dispensing facilities

Seals must be provided at the classification boundaries to minimize the passage of flammable gasses through the conduit system. Seals are provided at explosionproof enclosures to contain the explosion within the enclosure.
Don

[ May 25, 2004, 11:48 AM: Message edited by: don_resqcapt19 ]

 

[bnd]

Re: Motor fuel dispensing facilities

Don
I understand this, my ? is in a dispenser containment do we seal the gas's leaving the containment with the seal at the point of the conduit entering the containment or do we seal at the point of the entry into the dispenser.
I feel the latter is better because if an ignition is going to occur this is the ?most likely spot.
If you have a seal on the first fitting leaving the ground on the power end and a seal as the last fitting entering the dispenser J box, I do not see the need for the seal stated in 514.9 .
If you place the seal as to 514.9 and you have one-two & sometimes three capped elbows before you get to the dispenser J box. This leaves 3 chances for a mistake - a cross threaded cap or a forgotten cap ( witch I have came across more then once ) letting the gas's into the J box.
Why are we trying to keep the gas's out of a couduit that is sealed at the power end ??
BND

 

[rbalex]

Re: Motor fuel dispensing facilities

BND,

I must admit what threw me was that you did a verbatim quote for 514.9(A) but you ?free-styled? 505.16(A)(2). I realize the correct reference was 505.16(B)(2) and you may want to re-read it. BTW are you really installing to a Zone rather than Division classification system?

In any case, using 505.16(B) (2) indicates the enclosures under consideration are Division ?explosion-proof? rather than Zone protection type ?d? or ?e.? In this case only arcing, sparking, or heat producing (ASH) devices are considered unless the conduit is 2? or largerand the enclosure contains terminals, splices, or taps. Even if the seal is required because of one of these conditions and not otherwise exempted through an exception it still can be as much as 18? from the enclosure. The required boundary seal may be as much as 10? from the boundary. In other words, the enclosure seal and the boundary seal may, in fact, be the same seal.

BTW in this application gases will get into the conduit ? period. (They will get into the explosion-proof enclosures too.) However, if everything is sealed properly there will be no ready source of ignition (no ASH) in the raceway. Conductors properly sized will not generate enough heat to ignite the gases in this application, which are typically Group D (or IIA if you?re using Zones).

[ May 26, 2004, 03:26 PM: Message edited by: rbalex ]

 

[bnd]

Re: Motor fuel dispensing facilities

Bob
Nice name, Same as mine.
I agree that there is no ready source of ignition in the conduit raceway, but the chance of a hot wire slipping out of a wire nut and arking is a real posibleity.
I there for beleve the seal would better protect the system if placed at the entry of the dispenser splice box with any unions or caped elbows on the suppy side of the seal.
I do not understand the code reasoning on this.
Bob/BND

 

[rbalex]

Re: Motor fuel dispensing facilities

Extracted from 505.16 FPN No.1:

Seals are provided in conduit and cable systems to minimize the passage of gases and vapors and prevent the passage of flames from one portion of the electrical installation to another through the conduit. ?. Unless specifically designed and tested for the purpose, conduit and cable seals are not intended to prevent the passage of liquids, gases, or vapors at a continuous pressure differential across the seal?

The first part is what Don pointed out in his response. It is important to note that, depending on its location and use, a given seal may only provide for one of the functions.

The second part of the quote is important for ?explosion-proof? equipment ? most poured seals are NOT ? ? specifically designed and tested ? to prevent the passage of liquids, gases, or vapors??

As I said in my first response gases WILL get into both the conduit and enclosures. You are correct that a loose connection at a terminal could cause an arc inside the enclosure. That is exactly what an explosion-proof enclosure is designed for - to contain a possible internal explosion ? not prevent it. What it was designed to prevent is the propagation of the explosion to the outside. This covers the second function; i.e., ?? prevent the passage of flames??

Note the first function is to only ?? minimize the passage of gases and vapors?? Placing the boundary seal such that no other fitting is between it and the boundary minimizes but does not prevent the migration of ignitable materials.

Oh yeah, you still didn't say whether you were really using Zones or not

[ May 27, 2004, 03:35 PM: Message edited by: rbalex ]

 

[don_resqcapt19]

Re: Motor fuel dispensing facilities

BND,

Conduit seals shall be installed within 450 mm (18 in.) from the enclosure. Only explosionproof unions, couplings, reducers, elbows, capped elbows, and conduit bodies similar to L, T, and Cross types that are not larger than the trade size of the conduit shall be permitted between the sealing fitting and the explosionproof enclosure.

The explosionproof fittings that are used in the 18" or less of conduit between the enclosure and the seal will contain the hot gasses within the conduit system. If the dispenser is more than 18" from the point where the conduit emerges from the ground, 2 seals will be required. If the conduit length will be 18' or less, it is possible to use a single seal.
Don

 

[rbalex]

Re: Motor fuel dispensing facilities

Don,

You are actually allowed up to 10' from the boundary 505.16(B)(4)

Bob

 

[don_resqcapt19]

Re: Motor fuel dispensing facilities

Bob,
You are correct as long as there are no threaded fittings between the boundry and the seal. I guess the point that I was trying to make is that the enclosure seal must be within 18" of the enclosure and that in some cases, this may require the use of two seals and in other cases, you can make a code compliant installion with a single seal.
Don

 

[stew]

Re: Motor fuel dispensing facilities

I must be somewhat confused. I have always installed a boundary seal and a seal at the 18 inch point as well. I was under the impression that a boundary seal was always required.No?

 

[don_resqcapt19]

Re: Motor fuel dispensing facilities

Stew,
If there are no threads between the boundary and the seal, it can be up to 10' from the boundary. I see no reason why a correctly located seal cannot serve both functions.
Don

 

[rbalex]

Re: Motor fuel dispensing facilities

Under certain conditions for Zone 2 (and Division 2) you may not need a conduit boundary seal at all. See 505.16(C)(1) Ex 4 and its Division counterpart 501.5(B)(2)Ex 4.

I'm rather proud of those. I was the initial editor of the Division exception with the endorsement of API. John Rannels was the originator of the concept. I developed the "conditions" and Dave Bishop did the primary wordsmithing.

I was the actual originator and wordsmith of the 10' rule for both Division 1 and 2 (and their subsequent Zone counterparts). Before then there was no distance specified and 18" was commonly thought (erroneously) to be the requirement.

Technically, as long as there are no additional threads, it could be any length. We settled on 10' only because it is the length of a standard stick of conduit. UL listed conduit can, in fact, be any manufactured length.

I was also the originator of the "listed explosionproof reducers at the conduit seal" exception in the main rule.

All API proposals were made at the time by the Chairman of their Interdepartmental Advisory Group.

[ May 28, 2004, 06:34 PM: Message edited by: rbalex ]

 

[bnd]

Re: Motor fuel dispensing facilities

Bob
Don't understand your ? about using Zones.I'm running conduit from the power source inside a building to the sump located under the fuel dispenser and then up to the fuel dispenser. So I would say it would be a Class 1 Zone 1 type D & E,but I'm not totally sure. How does this come into play with what I'm doing?
Now as to your explosion-proof enclosure scenaro.If you don't have a seal at the first fitting leaving that enclosure and a capped elbow cover has been left off, would not the ignited gas extend itself through the missing cover and ignite the gases in the sump. By not having a seal at the J box you leave to much to human error. A poured seal must be cut off, but an elbow cover just unscrews.


Don
If a seal is required on the first fitting entering the dispenser sump (the boundary)and by the time you wind the conduit around the gas lines to get the dispenser J box, a second seal makes sense.
I still have double understanding the need for the first seal at the sump end.Now the seal at the first fitting leaving the ground or cement at the power end of the conduit makes sense, but what does the one at the sump end accomplish? If as Bob says, seals do not keep gases out, and you say that seals are to contain the explosion with in the enclosure and a conduit run sealed at each end is in fact an enclosure.Where does the possibility of an explosion in this enclosure exist? What is your igniting source? Why can't this enclosure be extended to a seal entering the dispenser enclosure ( J box ). I see no ignition potential between these two points.
BND

 

[don_resqcapt19]

Re: Motor fuel dispensing facilities

bnd,

If a seal is required on the first fitting entering the dispenser sump (the boundary) and by the time you wind the conduit around the gas lines to get the dispenser J box, a second seal makes sense.

If the conduit length between the J-box and the entry seal is 18" or less and all the fittings are explosionproof a single seal is permitted.

If you don't have a seal at the first fitting leaving that enclosure and a capped elbow cover has been left off, would not the ignited gas extend itself through the missing cover and ignite the gases in the sump.

Human error is always possible. The same thing will happen if the junction box cover is not tightly screwed on or if all of the junction box cover bolts are not properly torqued. Bolts that are either too tight or too loose will result in a small gap where gasses that are hot enough to ignite a flammable atmosphere can escape.

Where does the possibility of an explosion in this enclosure exist? What is your igniting source?

If the insulation of a conductor is damaged at the time of installation, this damage may not show up for a period of time. If the atmosphere in the conduit is within the flammable range at the time of the conductor failure the seal is needed to confine the explosion to the raceway. Flaming gasses escaping into the interior part of the dispenser is not a good thing.
Don

 

[rbalex]

Re: Motor fuel dispensing facilities

Bnd,

In my first reply, I asked if you were actually using Zone rather than Division electrical area classification. I was referring to that original query in my next reply. It is now clear you are indeed using Zones. In that case, I?m curious what standard was used to develop the electrical area classification since Article 514 doesn?t recognize Zones. In fact, you can make a very strong case that the sump beneath the dispenser is Zone 0.

In any case, for this discussion, let?s simply assume the entire area classification was developed from 514.3(B)(1) with Zone 1 = Division 1 and Zone 2 = Division 2. Let?s also assume the dispenser is listed per UL 87. That covers a lot of internal wiring issues that we won?t have to deal with here. I am also making a final assumption that all field wiring is through the terminal box in question and only terminals are actually in the enclosure. Clarify if any of these assumptions is incorrect.

Don and I have both made the point that a single, properly installed, seal may cover all requirements for both flame propagation and gas migration reduction. Those requirements are that the flame propagation seal be no more than 18? from the enclosure and all intervening fittings between it and the enclosure be identified for the area classification. Second, the boundary seal can be as much as 10? from the boundary, but no intervening threads, except an explosion-proof reducer at the seal, is permitted between the boundary seal and the boundary. If either of these conditions are not met, two seals are required.

I would also like to add one thing to the list of potential human errors/hazards Don pointed out. For an otherwise properly installed enclosure, a single scratch on the ground surface of [edited here] a ground-flange type cover may be enough to destroy the enclosure. Most ?type d? enclosures actually use threaded covers but flanged type are also recognized. BTW if the enclosure is only ?type e? and not ?d, e? an internal ignition, though rare, could still be propagated externally and no seal would stop it.

[ June 01, 2004, 10:21 AM: Message edited by: rbalex ]