Electrical Repair Questions? Ask an Electrician for Answers ASAP
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1) Will the sub-panel be located within the same building as the main electrical panel or will it be installed in a detached building from the main electrical panel?
2) What is the distance from the main panel to the sub?
3) I am unable to view any pics, they were not attached to the question.
4) Is the sub-panel a main breaker or a main lug panel?
1) Based on the pics, It appears that the sub-panel has a 100 amp breaker, if so that is good as this is a requirement for a detached bld'g. Detached bldg's require a main breaker sub and subs installed in an attached bld'g are OK to use a main lug sub.
2) Terminate the 2 hot feeds at the main panel via a 100 amp double pole breaker. Identify and tape each hot feed conductor with black and red tape respectively. Tape the neutral feed with white tape at each end. The main panel needs an Equipment Ground Bar for the Equipment Grounding Conductor going out to the sub.
3) At the detached bld'g, you need an 8 foot ground rod using 8 AWG Copper connected to the sub equipment ground bar. The sub needs an equipment ground bar and must be isolated from the neutral in the sub. If the sub has a green bonding screw or copper bonding jumper, this needs to be removed since the neutral must float in a sub and not be bonded to the sub's metal enclosure. Connect the 2 hot feeders from the main panel to the hot bus bar lugs on the sub. Connect the neutral feeder at the sub to the neutral bus bar. Connect the Equipment Ground Conductor from the main, to the Equipment Ground Bar in the sub. Connect any bare copper Romex grounds to the Equipment Ground Bar in the sub. Do NOT mix grounds and neutrals in the sub's neutral bus bar, they must be separated.
4) The voltage drop for the run using 2 AWG copper is only 5.82 volts which is OK. 4 AWG for the Ground is OK but you only needed 8 AWG. Not sure if you will run Underground Feeder or conduit to the detached bld'g. If UF cable - OK. If conduit, suggest using gray electrical PVC. If conduit, the conductors must be moisture resistant using type THWN Copper. I assume you are using copper for your conductors, if using aluminum, let me know. If using conduit, do not use type THHN as these are not moisture proof.
Hope this helps.........If you have any additional questions, let me know and I'll be glad to answer them for you.
Otherwise, don't forget to rate me before you log Off.The next time you have an electrical question, you can also request for me at:http://www.justanswer.com/home-improvement/expert-your-electrician ..........Thanks..............Kevin!
1) Yes, thats correct, the sub needs a separate grounding bar to connect any equipment grounds such as bare copper Romex wires or green wires as well as the Grounding Electrode Conductor to the ground rod. Grounds and Neutrals in all sub's must be isolated from each other. The only time the grounds and neutrals are bonded together is at the main electrical panel via the green screw or copper main bonding jumper and never in a sub. If you do not isolate the ground and neutrals in a sub, it presents a potential safety hazard.
2) The main also needs its own ground bar. These ground bars cost around $6 each and can be purchased at any of the big box home improvement stores. The ground bars can be located in any convenient area of the main and sub-panels on the back where the bus bars are located. Best area to locate them is either to the left or right of the neutral bus bar or towards the bottom of the panel. The 2 holes for each ground bar will need to be tapped at the back surface of the panel metal enclosure due to the threaded machine screws. Depending upon the panel manufacturer, some panels will have these holes pre- tapped from the factory.
3) The 2 hot feeder wires only get connected to the respective circuit breakers @ each panel. The hot feeders DO NOT get connected to a neutral and/or ground bar. Hot wire feeders only land on a breaker, nothing else. Neutral wires, white or gray only get landed on a neutral bus bar, nothing else. Ground wires only get landed on an Equipment Grounding Bar, nothing else. The Grounding Electrode Conductor from the 8 foot ground rod gets landed on the equipment ground bar inside the sub-panel.
4) At the sub, DO NOT mix bare copper grounds and neutrals on the same bar. They both need to be on separate bars.
1) You are correct on everything except the aluminum wire sizing. For a 100 amp sub-panel feeder the 2 hots and 1 neutral need to be either 2 AWG Copper or 1/0 Aluminum.
2) The Equipment Grounding Conductor connecting the ground bars need to be either 8 AWG Copper or 6 AWG Aluminum. The Grounding Electrode Conductor to the ground bar needs to be 8 AWG copper or 6 AWG aluminum. I recommend using 8 AWG copper to connect to the ground rod since Aluminum wire cannot come in contact with the earth @ the ground rod clamp.
3) Underground Feeder (type UF) is OK for direct burial and is underground rated. When backfilling the trench, you also need a red ribbon tape. These are a red ribbon that shows that live wires are underneith the red warning ribbon tape. The red warning ribbon is typically placed at a few inches below grade level. In general, UF cable must be buried a minimum of 24 inches below grade. The red warning ribbon is also available at Home Depot or Lowes or any electrical supply store. They come in a roll of a few hundred feet or so. The red warning ribbon is required in the event that anybody digs along the path of the UF cable. When they reach the red ribbon tape, this will warn the digger that there are live wires below.
4) You mentioned that you would be using 2-2-2-4. If using aluminum conductors, they must always be sized one size larger than copper due to their resistance per foot which equates to the proper voltage drop and current carrying capacity. Copper is always a better current carrying conductor but also more costly. But aluminum is widely used such as your application due to the distance involved, thus a more cost effective solution than copper.
1) Hot wires can be any color except white, gray, green, bare copper or yellow with a green stripe. Yes, typically hot wires are usually black, blue or red. Black being the most common as a hot conductor.
2) For a feeder circuit such as a sub, the neutral wire can either be black, white or gray. If using black as the neutral feeder, the black cable needs to be re-identified using white tape at each end. At the branch circuits ,the neutral can only be white or gray, no other colors allowed.
3) Ground wires can be black, but they must be re-identified using green tape on each end. Or bare copper or green color can be used.
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Take care and have a great evening.....Thanks.............Kevin!