Short answer: the hub is not the weak link, the listing is. A Myers hub — the trade name the field uses for a threaded sealing hub with an O-ring, a locking nut and a bonding screw — is listed for rigid metal conduit (RMC) and IMC only. Thread a PVC male adapter into one and you get a tapered thread sealed by sealant, about Type 3R quality at that entry, and a bonding screw with nothing to bite. Your utility casts the deciding vote: most US utilities specify IMC or RMC for the service riser, which settles it for metal. Where PVC is allowed, drop the metal hub and use a listed nonmetallic hub, or a male adapter with a sealing locknut.
What the hub is listed for
The hub earns its keep on steel. Its listing covers RMC and IMC, indoors or out, and it is listed for service-entrance raceways in that use. The nut's teeth and the hub shoulder bite into the enclosure wall. The tapered thread makes up metal to metal with the conduit. The bonding screw ties hub to box, so conduit, hub and enclosure carry fault current as one body, which is what NEC 250.96(A) asks of metal parts serving as the grounding path.
The hole is standardized as well. UL 50's fitting table (Table 71-1A, 13th edition) fixes the knockout diameter each trade size of hub must fit, so a 2 in hub drops into the same hole on any listed box. If your question is really about hole and thread fit rather than conduit material, threaded hub connector compatibility for outdoor boxes covers that side.
What a PVC male adapter gives you in it
Screw a PVC male adapter into that hub and every feature above goes quiet. The 2 in NPT thread tapers 3/4 in per foot, so the joint does tighten as it seats. On plastic, though, the seal is your thread sealant rather than metal-to-metal contact, and plastic threads creep under the daily temperature cycle a sun-loaded riser sees. The bonding screw finds no metal to bite, and cranking it only puts hoop stress into the adapter, which turns up later as a crack at the last thread.
What you are left with is a joint about equal to a male adapter under a sealing locknut: rain-tight in service, roughly Type 3R at that entry, on a box that is rated by its weakest hole. The hub vs sealing locknut comparison for outdoor top entries works through that choice, and running PVC conduit into an outdoor enclosure covers the rest of a plastic entry.
The riser: the utility decides first
Call the serving utility before you buy either hub. Most US service specifications name IMC or RMC for the riser, and several accept PVC only in schedule 80 wall where it stands exposed to damage. Canadian installs sit under a different code, and PVC service raceways are common there where the utility accepts them. On a metal riser the question dissolves: Myers hub, listed assembly, done.
Bonding follows the raceway. With metal, the hub screw and the conduit are the path. With PVC the metal ends at the box, so your copper equipment grounding conductor inside the raceway does the work. It is sized from the overcurrent device ahead of it by NEC Table 250.122: 6 AWG copper on a 200 A main. The earth carries no fault current under NEC 250.4(A)(5), so the ground rod beside the riser adds nothing here. For metering cabinets specifically, CT metering bonding before the service disconnect lays out the terminations.
One caution before you open anything on this wall: service gear stays live at the line lugs with the main off. Lock out, verify absence of voltage, and let the utility pull the meter when the job needs it.
How much water sits above a leaking entry
Run the arithmetic and you will treat the top entry with respect. A 2 in schedule 40 riser has an inside diameter of 2.067 in [52.5 mm], so its cross-section is pi/4 x 2.067 squared = 3.36 sq in [21.7 cm2]. Ten feet [3 m] of it holds 3.36 x 120 = 403 cu in, which is 6.6 L [1.7 gal] of water parked above the hub. A weeping thread delivers that straight onto the lugs. The box's own rating stops at its gasket: an IP66 enclosure earned that mark against 12.5 mm nozzles at 100 L/min from 2.5-3 m, entries in place.
Heat makes the joint move. PVC grows about 4 in [102 mm] per 100 ft per 100 F swing, roughly five times steel's 0.8 in [20 mm], and a dark riser in the sun cycles that daily. That is the mechanical case for a gasketed hub body over a bare sealant thread, and it is why 3R gear leans on a 3 mm [1/8 in] weep at the bottom. NEC 314.15 allows openings of 3 to 6 mm [1/8 to 1/4 in] in boxes listed for damp or wet locations. Water already inside a cabinet usually came through an entry; the unsealed conduit entry repair checks walk the hunt.
What to order for each case
For what 3R, 4 and 4X each promise at the gasket, the NEMA 4 vs 4X guide holds the fundamentals. Your decision at the top entry:
| Riser the utility allows | Entry to order | Seal you keep | Bonding path |
|---|---|---|---|
| IMC or RMC (most US utilities) | Myers-type hub on the metal thread | Full gasketed hub seal; entry holds the box rating | Hub bonding screw bites the conduit (NEC 250.96(A)) |
| PVC, box must stay sealed | Listed nonmetallic hub: PVC body, O-ring, clamping ring, glued to the conduit | Gasketed hub seal, same class as metal | Copper grounding conductor in the raceway (6 AWG for 200 A) |
| PVC, 3R is enough (meter can) | PVC male adapter + sealing locknut | About Type 3R at that entry | Copper grounding conductor in the raceway |
If the enclosure is on your order too, match the grade to the site. 304 stainless covers most outdoor walls and indoor washdown; choose 316L where the riser sits in salt air or chlorides, since 304 can pit under chloride deposits even at room temperature. A 24 x 24 x 8 in [610 x 610 x 203 mm] box takes a meter-adjacent junction layout with room for the bonding block, in 304 stainless or 316L. Our wall-mount boxes are rated NEMA 4X / IP66 by the manufacturer; not UL listed, and NEMA does not test, certify or endorse enclosures. For a size, material and cutout the catalog does not carry, custom enclosures are built from one piece and delivered in 10 business days.
Enclosures in this article
| Enclosure | Material | Outside H x W x D / display | Rating |
|---|---|---|---|
| 24 × 24 × 8 in | 304 stainless | 24 x 24 x 8 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
| 24 × 24 × 8 in | 316L stainless | 24 x 24 x 8 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
Questions
Can you thread a PVC male adapter into a Myers hub?
Installers do it constantly and it usually holds, but the hub's listing covers rigid metal conduit and IMC only, so it is not a listed assembly. What you get is a 2 in NPT thread (taper 3/4 in per foot) sealed by thread sealant, about Type 3R at that entry. Where the inspection runs strict, the listed fixes are a nonmetallic hub or a metal riser.
Why does the bonding screw do nothing on PVC?
The screw exists to bite a metal raceway so that enclosure, hub and conduit carry fault current as one path, which is what NEC 250.96(A) asks of metal parts serving as grounding conductors. Plastic gives it nothing to bite, and tightening it only adds hoop stress to the adapter. The fault path then rides the copper grounding conductor inside the raceway: 6 AWG copper for a 200 A main from NEC Table 250.122.
Will the power company allow a PVC service riser?
Many will not: most US utilities specify IMC or RMC for the riser, and several accept PVC only in schedule 80 wall where it is exposed to damage. The serving utility's spec decides before you buy anything, and switching after the rough-in costs you the riser, not just the hub.
How much water can a leaking top entry let in?
About 6.6 L [1.7 gal] in the common case: a 2 in schedule 40 riser 10 ft long holds pi/4 x 2.067 in squared x 120 in = 403 cu in. A weeping thread delivers it onto the lugs, which is why 3R cans carry a 3 mm [1/8 in] weep hole at the lowest point of the bottom, never near a live terminal.
What hub keeps a 4X rating with PVC conduit?
A listed nonmetallic hub: a PVC body with its own O-ring under the shoulder and a clamping ring inside, glued to the conduit. Two checks make or break it: the box cutout must match the hub's trade size, since UL 50's fitting table fixes the hole diameter per size, and the solvent weld must be fully seated before energizing, because an unseated joint leaks past the ring. On this site the boxes are rated NEMA 4X / IP66 by the manufacturer; not UL listed.
