Concentric and Eccentric Knockouts: Which Need Grounding Bushings?

hey this is Bill for Sparky Channel today I got a question from a viewer Sparky can you do a video on concentric and Ecentric Knockouts and which needs a ground bushing yeah I can do that let's start out with exhibit 100.5 from the 2023 anyc handbook the handbook has all the articles that the regular codebook has plus it has drawings like this and notes and explanations so this is exhibit 100.5 the picture on the right shows a concentric knockout on the top and a Ecentric knockout on the bottom and the picture on the left shows bonding jumpers and what they might look like this is a note that found in the 2023 handbook and let's start right where the arrow is there bonding jumpers are particularly important where a box has either concentric or Ecentric type knockouts these Knockouts can impair the electrical conductivity between metal parts and may actually introduce unnecessary impedance into the grounding path these concentric and Ecentric Knockouts can be found in panels and electrical boxes of All Sorts this is 250.92 b b is method of bonding at the service bonding jumpers meeting the requirements of this article shall be used around impaired connections such as reducing washers or oversized concentric or accentric Knockouts standard lock nuts or bushing shall not be the only means for the bonding required by this section but shall be permitted to be installed to make a mechanical connection of the raceways electrical continuity at service equipment service raceways and service conductor enclosures shall be ensured by one or more of the following methods one bonding equipment to the grounding service conductor by an applicable method in 250. 18a two connections made up wrench tight using threaded couplings threaded entries or listed threaded hubs on enclosures three threadless couplings and connectors if made up tight for the metal raceways and metal clad cables and for other listed devices such as bonding type lock nuts bushings or bushings with bonding jumpers here is an example of Ecentric Knockouts you see here's a smaller Circle here and a larger circle out here and then this would be our 2-in knockout right here and that's what our contestant did he uh knocked out a 2-in knockout and this is a plastic bushing to help the cables to not get damaged when they're pulled through the nipples here we have two 12in metal nipples connecting the three panels all four of the connections have eccentric Knockouts which are larger than the 2-in knockout which was used let's examine each connection to find out which connection should have the grounding bushing let's first take a glance back at the code electrical continuity at service equipment service raceways and service conductor enclosures shall be insured by one or more of the following methods here in article 100 we have definitions and here's the word service and it means the conductors and Equipment connecting the serving utility to the wiring system of the premises served and then we have service conductors which are the conduct doctors from the service point to the service disconnecting means here's a drawing from the 2023 handbook that shows the service point it shows Underground Service conductor it shows service entrance conductors and it shows a meter and service equipment and our example has a meter socket very similar to that with no disconnecting means in the meter here we are at NEC 2023 3 250.24 B loads side grounding connections a grounded conductor shall not be connected to normally non-current carrying metal parts of equipment to equipment grounding conductor or conductors or be reconnected to ground on the load side of the service disconnecting means except as otherwise permitted in this article so we're clearly looking to put our grounding pushing on service conduit the service entrance conduit coming into the meter socket is made of rigid PVC so we can't put a grounding bushing on that how about this connection right here this is clearly service conduit it and there are Ecentric rings in this connection however there is no ground going to this particular meter socket so we can eliminate this connection from needing a grounding bushing how about this connection which does have Ecentric Knockouts well this is not service equipment this is on the load side of the service disconnecting means which is this big switch right here so this connection does not need a grounding bushing so that leaves these two connections which do have Ecentric Knockouts here's how one contestant handled it he put the grounding bushing on the left hand side and this is the middle paddle which is the the safety switch notice the ground wire comes in from the load Center there is no ground wire coming from the meter socket the meter socket is bonded because the neutral lug in the meter socket is bonded to the enclosure this nipple is on the load side of the surface disconnecting switch so it is the feeder or branch circuit side and does not require bonding this n which comes from the meter socket is on the service side and is required to be bonded this is the nipple that needs the bonding bushing because it is on the surface side of the main disconnect and we have Ecentric Knockouts there so it is required to bond this nipple this is how one contestant placed his grounding bushing in the panel with the service disconnect he did a nice job of installing the grounding bushing and running the ground wire through the grounding bushing lug but he has his grounding bushing protecting the loads side nipple instead of the servide nipple here is what another contestant did with his grounding bushing he successfully put it on the service side with the Ecentric Knockouts which is correct however for whatever reason he didn't get the ground wire run into the grounding bushing lug and then to the Ground Bar of the panel here you can see how you strip off about an inch of insulation off of the ground wire and put it into the grounding bushing lug I would also like to mention that there are some special rules for bonding over 250 volts to ground our system in the example was 240 volts in conclusion if I had one 2-in grounding bushing to work with I would put it right here of course you can put more grounding bushings if you like it's okay to exceed the code so what do you guys think where would you put your one grounding bushing I hope this video was helpful thanks and happy [Music] wiring a

Channel: Sparky Channel

Views: 4,840

Keywords: Sparky Channel, Sparky, electrical, electrical tools, electrician, NEC 334.30 (B), NEC, electrical codes, NEC handbook, 334.30, National Electrical Code, Electrical Code, NFPA 70, National Electrical Code (NEC) Handbook, DEWALT DCN701D1, DeWalt cable stapler, cable, NEC 330.30, NEC 330.30 (D), code changes, 314.16 B 2, box fill, NEC 314.16, Marked Controlled Receptacles, NEC 406.3(E), Leviton 16252-1PW, 2023 NEC, 2023 NEC code book, 2023 handbook, grounding bushing

Id: IV-ka0eXs84

Length: 8min 37sec (517 seconds)

Published: Mon Feb 26 2024