Questions wire size for subpanel, receptacle orientation

[sleepy hollow]

1) I am adding a 100 amp subpanel in my basement. Is #4 copper sufficient (it's actually #4 SER with two hots, a neutral and bare ground)? I believe it is ok, just wanted another opinion.

2) I have noticed that in new commercial construction the receptacles are being installed "upside down", that is, with the ground prong slot up. Is this something req'd by code now? If so, why? Should I do this in my basement when I finish it out?

[Rich]

Typically the upside down plugs are only to distinguish a plug that is switched - such as for floor lamps.
#4 cu should be just fine... how far as the run from main panel to subpanel?

[sleepy hollow]

1) It's about 10-12 feet at most (just down from garage to basement though rim joist and over a couple feet to panel) so almost no voltage drop.

2) In this case every receptacle in the building is wired upside down. Definitely NOT an indication of switched outlet. Interesting...

thanks

[Rich]

1- You shouldn't have any trouble with #4 at that distance.
2- can't say that I've seen a whole project with them upside down.

[sleepy hollow]

Much obliged for your help.

[ndemge]

I notice the ubpside down ones a lot, and it anoyes the heck outa me.

[Vector]

There is no such thing as "correct" orientation for a standard 120V receptacle. You could mount then at a 45 degree angle and it would be legal.

But, that said, there are some reasons to mount them particular ways.

What most people think of as "right" is where the neutral is on the upper left, the hot in on the upper right, and the ground is below, and it looks like a face. This works better in some cases, because a lot of plugs and extension cords with a 90deg bend are designed to hang correctly this way.

What most people think of as "upside-down" is with the ground on the top and the hot on the lower left, and the neutral on the lower right. This is very common in commericial settings. This is arguably a little bit safer than the other way. If a thin metal object falls down and lands between the receptacle and plug, it will make contact with the ground. If the plug was the other way around, it could contact both the hot and neutral and short-circuit, or worse yet, just the hot, and become energized and a shock hazard to anyone going to pick it up. I mount receptacles this way unless there is a reason not to (appliance cord that won't hang right, etc).

When a receptacle is mounted on it's side, it should, in my opinion, always be mounted with the neutral (wide slot) up to protect from dropping things onto the hot conductor.

[Vector]

#4 Copper is fine for the sub-panel.

One thing a lot of people don't realize is that in a sub-panel the neutral and grounds must be separated.

With most panels, this means removing the green screw that bonds the neutral bar to the chassis of the panel, and adding a separate ground bar (generally sold for a few bucks right next to where the panels are).

[Tom R]

As Vector stated the 'upside-down' orientation is in case of falling metal (I don't know what the odds of that are), but I have heard this will become 'code' in the near future. Vector, - - funny you should mention about the face, - - that's the way I always thought of it, - - anyway, one time a buddy was using a heat-gun to dry the spackle faster around the receptacle, - - and he didn't realize he let it get too hot until he saw the SAD-FACE!! :( LMAO! - - while he changed the recep!

[sleepy hollow]

Thanks. I was aware of the neutral/ground separation. I bought a Square D Homeline box which actually requires a separate ground bar. They supply a green bonding screw which I will NOT install to keep the neutral bus isolated from the box and ground.

As for the receptacle orientation, it occurs to me that this would have worked nicely for my toddler niece who recently scared her parents when she tried to stuff a penny down behind a plug into a wall socket. Thankfully she droped the penny and it shorted the receptacle without her in contact, but could have been much woirse. The only problem here is that they have older ungrounded wiring in this part of the house, so it is only a 2-pronger. But, it gives me pause. I am not old enough yet, but at some point my kids will be having children (hopefully) and I will want them to play worry-free in grandpa's basement...hmmm.

[Vector]

One other thing, if the basement is unfinished, all outlets must be GFCI protected.

And that's even better protection in the situation you describe above with your niece.

And you can replaced ungrounded outlets with GFCI outlets. It's not only the only code legal way to have a three-prong outlet without a ground wire, but it provides all the same protection as a GFCI on a grounded circuit (it does not provide a true ground for use with devices like a surge supressor, however).

If they could figure out which outlet is the first in the series, only that one would have to be replaced with a GFCI, and all the rest could be changed over to 3-prong (or left as is, if a 3-prong outlet was not needed).

As a child I was always curious about electricity. With GFCI, my childhood would have been a lot less "eventful" :shock: :shock: :shock:

[sleepy hollow]

This is great information. My brother-in-law had asked me what they could do and I was stumped.

So, if you do not mind, I want to understand better, and have some follow-up questions:

1) I basically understand GFCI, but could you help me understand how it would have helped in the case I described with my niece? That is a good specific example and would help me convince my B-I-L to retrofit.

2) How is it that adding a GFCI (either at a particular receptacle location, or "upstream" from others) now allows me to use a 3-prong receptacle? Is the ground plug not used? I am missing something.

3) Also, how about the fairly new arc interrupters (cannot quite recall the acronym)? Whould one of those be installable/useful?


Thanks.

[Vector]

1) A breaker only trips when the amount of current on the circuit exceeds the rating of the breaker by a cretain amount over a certain period of time. The breaker tripped very quickly in this case, but had your niece still been holding the coin, she could still have gotten a dangerous shock. Worse still, had she been holding the coin and touched only the hot conductor, she would have gotten a very nasty, and potentially fatal shock. The same would hold true if a child poked a paperclip into the hot side of an outlet.

A GFCI trips when there is as little as 5 milliamps of power differential between the hot and neutral lines. This wouldn't change things if all you had was a straight short across the hot and neutral, as you had, but had she been touching that penny, and any current had passed through her body to ground, it would have tripped before it could harm her. In the case where only the hot side is contacted, the main breaker does no good at all, but the GFCI will trip before any hazardous amount of current can flow through the person coming into contact.

The way to look at this is that circuit breakers/fuses are there to prevent fires. GFCIs prevent shocks.

I don't have any more time right now, but I'll address #2 and #3 later.

[Vector]

Bet you thought I forgot :)

2) How is it that adding a GFCI (either at a particular receptacle location, or "upstream" from others) now allows me to use a 3-prong receptacle? Is the ground plug not used? I am missing something.

A GFCI has two sets of screws on the back, one is the "line" side, and this connects back to the supply. The other side is called "load" and provides GFCI-protected power to any device(s) attached to it. So a GFCI outlet can protect an entire circuit, as long as everything to be protected is connected after the GFCI. That much you probably already knew.

However, a GFCI does not need a ground wire to operate. It works by sensing differences is current between the hot and neutral wires, and doesn't do anything at all with the ground wire (the name comes from the fact that if there is an imbalance in current, then it is flowing to ground, not necessarily on the ground wire (or Equipment Grounding Conductor/EGC).

The EGC exists for two (main) reasons:

1. It protects you from electrical shocks. The classic example is a metal-chassis appliance, like a washing machine. If for some reason, the hot wire were to come in contact with the chassis, the chassis would become energized. If it is ungrounded, then if you touched the device, you could get a shock. If it is grounded, it will short out and blow the breaker/fuse. Now, you might think that you could do the same by attaching the neutral to the chassis, but you can't. The neutral wire carries current as part of it's normal operation, and as such is energized. You *can* get a shock from the neutral.

2. It allows a non-current carrying path to ground that is used by surge-protectors.

#1 is a safety reason, #2 is a convenience reason.

Since a GFCI outlet will interrupt the flow of electricity before dangerous current can pass, it provides the same level of safety as #1. The code is about safety, not convenience, so code allows you to replace an ungrounded 2-prong outlet with a GFCI. There still is no true ground in the circuit, but you are still protected. Since a GFCI provides protection to downstream devices, they also are safe without a ground, and can have 3-prong outlets installed. All such outlets (including the GFCI) should be clearly marked "No Equipment Ground." All GFCIs come with these little stickers, and that's why.

3) Also, how about the fairly new arc interrupters (cannot quite recall the acronym)? Whould one of those be installable/useful?

Arc-fault Circuit Interruptors (AFCI), work by sensing (and I don't know how) when an arc happens between hot and ground or hot and neutral, or even in-line on the hot. The primary value of these devices is to protect from damaged wiring, usually not in the walls, but rather appliance cords and extension cords. They can also help in the case of a loose wire on the back of an outlet (often caused by an overloaded circuit and overheating causing a wire to work loose due to thermal expansion/contraction). They are required for all bedroom circuits in new construction, since the bedroom is the place where you are most likely to be directly affected by an arc-fault (because it could start a fire while you are sleeping).

Personally, i think the current code is downright stupid about AFCI. If interpreted as written, then hard-wired smoke detectors also must be on the AFCI, and that's just a bad idea. I don't want something like my smoke detector to get shut-off by anything short of an actual short. Some localities allow the smokes to be on a non-AFCI circuit if there is nothing else on the circuit. Unfortunately, Minneapolis isn't one of them. I'll be wiring my smokes through an alarm system using low-voltage and a centralized battery backup.

[Tom R]

Hey Vector, GREAT INFO!!!

[sleepy hollow]

Many thanks for the great tutorial. It helps enormously. You are very kind.

By the way, I installed the 100 amp subpanel this past Saturday. Thankfully, the entire family was out for most of the day, and I was able to work in complete peace and take down the house power with no inconveniences.

Took about an hour and a half to do the following:

1) Clear area around main breaker and gather tools, prep
2) Remove main panel cover, review wiring and re-verify planned relocation of 2 20 amp circuits to make room for 100 amp 2-pole breaker to feed 100 amp main breaker in subpanel
3) "Cordon off" hot main line lugs (I used duct tape across the bottom quarter of the box to remind me to stay clear of the hot lugs)
4) Relocate 2 20-amp circuits from left side of panel to right side and combine into 2 tandem breakers
5) Remove appropriate size knockout for subpanel feeder cable and run feeder cable into box with clamp installed (#4 copper SER with 2 hots, a neutral and a bare ground) - this was tricky since the only knockout I could use was right next to the main feeder - up through bottom of box. I had to be very careful to stay clear of the hot lugs. Was very good that I had zero distractions and applied full concentration to this step.
6) Measure feeder cable component lengths, strip outer jacket, remove tape wrapping, and cut individual wires. I was able to cut the wires individually with regular lineman's piers, but it was not easy. My palms are still sore.
7) Install new lugs to neutral/ground bus large enough to accommodate #4 wire - required 2 adjacent slots for each wire, so I had to relocate 4 existing grounds/neutrals. This caused me to double up and triple up with other neutrals/grounds. Note in the main panel mixing neutrals and grounds is ok, but not in the sub.
8. Install ground wire first, then neutral, then hot wires to new breaker, then breaker to panel. Had to wrestle a bit with the wires to get everything to line up, as the #4 copper is loathe to bend easily, but I eventually won the struggle. Of course, I was also being very careful to stay clear of the hot lugs and took time before each maneuver to make sure that if I "slipped" I would not move in that direction.
9) Removed all duct tape barriers, rechecked wiring, checked tightness on clamp, made sure all new breakers were off, and replaced panel
10) Turned on main - no problems, then turned on all new breakers, except the 100 amp - no problems, the relocated circuits worked great.
11) Put duct tape over 100 amp breaker in "off" position and labeled it clearly to leave it alone. Just a precaution while I worked on the subpanel.

These 11 steps took about 1.5 hours.

Done and next moved to the basement where I mounted the box, wired it up, making sure to separate the neutral and grounds, that is, they are NOT bonded together.

I added 2 temporary 20 amp circuits for tools wired to different poles, and installed 20-amp receptacles.

Bottoned everything up and I am ready to move onto finishing the framing so I can make use of this new "unlimited" juice.

I was a very satisfying feeling. Overall cost - about $200 or less.