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Oleg
Premium
join:2003-12-08
Birmingham, AL
kudos:2
reply to Netkeys

Re: Dedicated circuit for a computer smart move or not

Another thing is the electrician has discovered that the breaker panel wiring was done wrong all the way around. When we have switched from the fuse panel to the breaker panel years a go. One thing i do not understand is why everything was working somewhat OK, but all of the sudden hell broke lose. Sparks were flying everywhere, and frying electronics. I am lost as why everything was OK for about 6 years.



nunya
Premium,MVM
join:2000-12-23
O Fallon, MO
kudos:12
Reviews:
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1 recommendation

Let me guess, multiwire branch circuits tied in incorrectly?

I've found houses where nearly every circuit was incorrectly wired. In essence, the neutral current on every MWBC was doubled.
I had one not long ago where the people had been there 10 years and not one neutral wire was brown or even discolored.
Ont he other hand, I've had them where the whole kit-and-caboodle is roasted after 3 months.

It all depends on the use. Some people get lucky.
--
If someone refers to herself / himself as a "guru", they probably aren't.



alkizmo

join:2007-06-25
Pierrefonds, QC
kudos:1

said by nunya:

I've found houses where nearly every circuit was incorrectly wired.

My bedrooms' MWBC had the two hot tied to the same leg. Fortunately I realized this quickly since I was snooping around my panel a lot. I've always wondered if the previous owners had this setup for 46 years (not much was changed over the years except a dishwasher circuit and central AC circuit, everything else is original).

whocares256

join:2002-03-10
Anna, TX
Reviews:
·DSL EXTREME
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·Callcentric
reply to Oleg

Depends on how much power you are using. I kinda asked this question in November. I have a laser printer that causes the lights in my office to flicker. I have CFLs in my house. Link to thread posted below.

»Electrical Derating

I have 3 options my self.

1: Leave everything how it is now.
2: Don't use laser printer
3: Install Dedicated circuit.

2 isn't an option and I'm doing 1 right now but eventually would like to get # 3 setup. I have the wire and tools and even the circuit breaker but am not sure how to run the wires. Breaker box is on outside of house. I also have a few NAS's now also. I would like to have a large 240v ups and whole house generator for backup of all the 120v circuits eventually. Don't know how piratical a large ups between when the power goes out and when a generator kicks in would be though. My house is new construction. (2012)



dib22

join:2002-01-27
Kansas City, MO
reply to IowaCowboy

said by IowaCowboy:

My computers are laptops and they share an outlet with a 120v window A/C in the summer.

Laptops have a built in UPS (the battery )


Oleg
Premium
join:2003-12-08
Birmingham, AL
kudos:2
reply to nunya

said by nunya:

Let me guess, multiwire branch circuits tied in incorrectly?

I've found houses where nearly every circuit was incorrectly wired. In essence, the neutral current on every MWBC was doubled.
I had one not long ago where the people had been there 10 years and not one neutral wire was brown or even discolored.
Ont he other hand, I've had them where the whole kit-and-caboodle is roasted after 3 months.

It all depends on the use. Some people get lucky.

I think this is exactly what was going on.


j cat

@verizon.net
reply to IowaCowboy

having an a/c or other motor device with electronic equipment is not good. I myself ran a 20 amp circuit to the room just for the a/c. the outlets in the room are only 15 amp so the a/c runs better now with a solid 20amp feed.

motors create surges and with laptop power supplies these do a good job reducing the surges created. still not a good idea to have both on the same line.

the electrical panel circuit breakers can be doubled. I installed a double 20 amp c.b. in place of the single 20 amp c.b.. works great. running the 12 GA romex is a bit of work.


F100

join:2013-01-15
Durham, NC

1 edit

1 recommendation

reply to Oleg

Residential power in the US uses "split-phase" transformers to deliver two 120 volt line to neutral legs that are 180 degrees out of phase from 1 leg of the three phase power system. The neutral leg coming out of the transformer is grounded at the pole or pad and again at your house at the service entrance where most of us have our only breaker box connected. The ground and neutral are both physically connected together here per NEC code.

If they added a dedicated 15 or 20amp circuit, the reason you don't need an isolated ground in this setting is that an outlet or circuit to a computer room already has a direct ground back to the service entrance. The idea is to have the neutral and ground only connected together at the 1st point of service which is your breaker box. Homes don't usually use metal conduit, boxes or face plates so the wires in the romex is the only source to carry the power. In a way, every circuity in a residential setting is an isolated ground.

There is nothing wrong with having a dedicated circuit if the extra expense is not an issue. You'll have less noise on the line have more head room for equipment. 14 gauge wire for 15amp or 12 gauge will allow 20 amp outlets. I have a a 120v UPS that needs a 30amp outlet. I'll have to run 10ga wire for this when I have time. I've also got some lines that I am going to split for these reasons I mentioned above. They tied to many rooms together in 1980 and I want them separate so that my fridge is not on my dinning room where my computer equipment is.



Oleg
Premium
join:2003-12-08
Birmingham, AL
kudos:2

1 edit

I agree. See someone has jointed two legs together when the electrician were looking at the breaker panel. In Europe 240V is a standard, but not in the US as you have mentioned. As budget goes we are on a low income, but it's better to be safe(r).



Oleg
Premium
join:2003-12-08
Birmingham, AL
kudos:2
reply to Oleg

I have taken a look at the work order on the invoice, and here what it's say's:

Troubleshooted sub-panel, separated neutral's from grounds.
Added 20 amp receptacle/branch circuit for computer.
General inspection of wiring


F100

join:2013-01-15
Durham, NC

1 recommendation

reply to Oleg

What happens in a Multi-wire branch circuit(MWBC) is that a line from each of the 120v "hots" if you will, shares the same neutral and ground wire. Because the two hots are 180 degrees out of phase, the current on the neutral wire is the difference between the two. If both lines are pulling 10 amps, 10-10 = 0 on the neutral wire. If one is 10amps and the other is 5, the neutral is carrying 10-5= 5 amps. The neutral never carries more than 1 fused hot alone can carry. On 14ga wire, the neutral should not carry more than 15 amps. But remember that neutral wires are not on breakers, only the hot.

If both hots get put on the same phase, then the neutral is carrying the sum of the current. 10+10=20amps This can cause the neutral to exceeded its current rating and overheat. Neutrals are not fused so there is noting to stop it from overheating as you plug more stuff into the circuit. That is why the problem shows up more now in older homes. We have more stuff plugged in which increases the load.

In my kitchen, the dishwasher and microwave share a MWBC. For appliance only outlets, they run the 3 wire with ground(black, red, white and bare or green) to save money. They split for the devices at the junction box. In residential it can cause issue like yours if someone doesn't know it was a MWBC. There can even still be potential on the neutral from the other line if you are working on a device and don't know it's a MWBC. That is why you are supposed to use breakers that trip both lines at once, forcing you to kill all power to a circuit when you turn it off to work on it.

In commercial, MWBC are very common since loads like light can be calculated and are fixed. With three phase motors, some don't even use a neutral, only three hot lines that are all 120 degrees out of phase.


F100

join:2013-01-15
Durham, NC

1 recommendation

reply to Oleg

Sounds correct. Sub-panels are supposed to keep the neutrals and grounds isolated until they connect back to the main service entrance panel. BTW, I'm not an electrician, I just learn how to do things the right way if I am doing it myself.



LazMan
Premium
join:2003-03-26
canada
reply to F100

Not everywhere is split-phase... NYC, for instance, typically delivers two legs of a 3ph Wye; so you get 120 phase to neutral, 208 phase to phase... (thanks Whiz... ) But you're right, centre-tapped single phase is the most common.

You're also correct that the ground and neutral are only to be bonded in one location - the service entrance; which may be BEFORE the main panel; or may be integrated into the panel, if it has a built-in disconnect. All sub panels (with a few specific exceptions) should have the neutral-ground bond removed...


scooper

join:2000-07-11
Youngsville, NC
kudos:2
reply to Oleg

If I had a laser printer - then yes, I'd want (and did) install dedicated PC circuits.

If I had an older house that didn't have grounding for each outlet and I needed a grounded circuit - it's probably easier to add a dedicated circuit for that as well.

Otherwise - while it won't hurt anything, I'm not sure you would really gain anything either.


westom

join:2009-03-15
kudos:1
reply to Oleg

The work order does not describe anything as serious as you originally described. As I read it, you have a main panel and a sub panel. The neutral and safety ground were miswired in that sub panel (as F100 said). A problem that was not serious.

Most circuits would be more than sufficient for that printer and computer (a tiny load). A receptacle (safety) ground is for human safety; not for hardware safety.

Isolated ground is often hyped due to hearsay. Unnecessary for any properly constructed electronics.

If any other circuit is powering a three prong appliance with only a two wire connection, then a breaker box CB (or receptacle) should be replaced with a GFCI.

BTW, all residential US power is 240 volts. With 120 volts derived from that incoming 240 volts.