Electrical Service Question

[wilbilt]

I'm not an electrician, although I have been known to dabble. A seriously outdated version of the NEC is a favorite bathroom reader...


My property is fed by a 100A single-phase 240VAC main panel. The source is an overhead feed supplied by a dedicated transformer on the pole out front. (i.e., it is "my" transformer, since I am the only subscriber connected to it.)

My main service panel feeds:

a. The house, which has a 100A subpanel inside.

b. A pumphouse, which is on a 20A 240VAC breaker, whose load is a small submersible pump that provides water.

c. A shed with a subpanel fed by a 50A 240VAC breaker. Loads connected to the shed include a 5HP 240VAC air compressor (something like 23A continuous when running), a 40A circuit for a welder (rearely used) and a couple of 15/20A circuits for lights and plugs.

When the compressor starts (magnetic starter), it causes a voltage drop noticable enough that the lights will dim in the house, and light loads like thermostatically-controlled box fans will actually stop.

The entire time the compressor runs, the lights in the house flicker. (mostly compact fluorescents). The fans, etc., will restart once the compressor shuts off. I haven't measured the actual voltage fluctuation, but I am ready to.

Will upgrading to a 200A main service panel help? If so, why? It seems that if the compressor is drawing enough current to max the current service, I would be tripping breakers. The feeders to the shed subpanel are #6 copper in a 35' run. The feed from the sub to the compressor is #10 copper, about 15'

Should I be more concerned about inadequate supply from the power company?

 

[PAToyota]

Although I also dabble and have a somewhat recent copy of the NEC for bedtime reading myself, I'm not sure I'm "expert" enough to weigh in on this.

I will say that when I upgraded my service from 200amp to 400amp (actually a C320 service) they had to upgrade the transformer to accommodate as well considering that neighbors across the street still have 60amp services and there are still many 100amp services while some 200amp services are slowly catching on... Since you have a "dedicated" transformer I'd be talking to the power company about its capacity. That may be part of the issue.

Another thing is that while I was still in college I picked up a 110V MIG unit that I was using in my parents' garage. We had some flickering lights and I was obviously drawing more power than the household was set up for - which confused my father since he had a 200amp panel put in special when he built the house and oversized the wiring and breakers for the garage. Checking into things found that even with the 200amp panel, the power company had only run wire for a 100amp panel from the road... The house was built in '69 and at the time they couldn't see that he would really need 200amp so they ran the same thing they ran everywhere else - to 100amp panels. All the time I was growing up, starting up my father's tablesaw would dim the lights throughout the house. After the upgrade there were never any further problems along those lines...

 

[wilbilt]

I was thinking about the wire size on the drop from the transformer as well. This property was originally developed in 1973, and I have no idea what size the conductors are.

They appear to be 00 aluminum (looking at them from the ground). I have been thinking about upgrading the panel anyway, because the existing one is a Sylvania/Zinsco and replacement breakers are priced as if they are solid gold (or copper LOL).

I'll grab my meter and get some actual voltage drop measurements at various points. Maybe they will give me a better idea as to where the problem lies.

 

[Vermaraj]

What is the distance from the transormer to the shed with the compressor? And, is the run primarily copper or aluminum?

Take the total distance and the starting load, which maybe as much as 2.5x the running load of 23amps, then use the voltage drop table in the NEC code book. Chances are you are dropping the voltage below 90V which will cause some motors to malfunction and may wear out your compressor prematurely.

If you're comfortable around electric panels you could measure the voltage across the sub-panel breaker in the shed with the compressor running.

Upgrading to 200amps will help if your normal lighting and appliance loads + compressor loads are actually above 100amps. If this were the case you would be reseting breakers constantly. If not you may have to run larger diameter wires to reduce the voltage drop (which will in turn reduce total # of amps drawn).

If the voltage is not unusually low you may have a floating ground or one leg of the main breaker may be bad. You would notice some lights may flicker or not light at all, except when a 230v circuit is in use. The 230v appliance will bridge the two legs and back feed the 120v circuits, a very dangerous situation.

 

[wilbilt]

Total distance from transformer to shed subpanel is about 85'. 50' aluminum drop to the main service and 35' copper feeder to the sub.

I am definitely going to measure voltage with the compressor running. I am comfortable working in live panels. Is there any other way? LOL

The only breakers that ever trip are the ones feeding the kitchen (microwave, electric rotisserie, and then the fridge starts up...)

I had an arced leg on one side of the main breaker several years ago, and replaced it. $150 ouch. None of those symptoms are present now. All grounds are solid and bonded to the main service ground with minimum #6 copper.

 

[mike944]

i had a similar problem once, it turned out to be a loose neutral connection. Aluminum wiring can get "loose" in the connectors over time. You can check it by wiggling the feeder wires anywhere there is a junction, but i would call an electrician to tighten them, unless you can disconnect them upstream of where the loose connection is.

With my loose neutral, when i turned on a heavy 110V load, half the lights in the house would get dimmer, the other half would get brighter. Took me over a month to figure out the problem. The heavy load would pull the netural away from zero, "toward" the line that fed that particular load. The electrical "distance" between the two would go down, while the "distance" between the other two would go up. I assume loose feeders could cause a similar problem. Check those before you go crazy trying to fix the problem.

 

[VDubJoe]

Call and have the local elect. co. come do a load ck. They will test it at the mtr. That will show if the problem is on their side or yours. They can also tell you the load capacity of the transformer they have installed. Alot of times the service drop is undersized and can induce flicker when startup loads occur. I troubleshoot for Progress Energy in Fl. I go on at least a dozen voltage problems a week caused by bad connections.
Hope this helps. Joe

 

[redsled]

Call and have the local elect. co. come do a load ck. They will test it at the mtr.

I work for the local EMC (for 21 years). What size transformer do you have 10,15,25 or what? Where are you located on the feeding of the line? I would atleast want a 15 kva transformer and #2 triplex. On your end I would put in a 200 amp panelnext to meter and feed the house with a 100amp breaker unless you change panel out inside your house. Then I would put the well connection in the outside box, and the shop. I would put the 100 amp panel if you removed it from the house to the shop with a #2 direct burial triplex feeding from the outside 200 amp disconnect this should let you do what you want in the shop and keep the wife happy.....Redsled

 

[wilbilt]

I work for the local EMC (for 21 years). What size transformer do you have 10,15,25 or what? Where are you located on the feeding of the line? I would atleast want a 15 kva transformer and #2 triplex.

I have no idea what the transformer capacity is. It is what PG&E refers to as a "Single Stand", and I am the only customer connected to the transformer. It is at the end of the line (the high-voltage lines stop here).

 

[David Hawkins]

How large of a subpanel can you run off a 200A service? My shop is in the process of being built and it will be 1800 square feet and support a wood shop and auto restoration work. I've got a 110V compressor that's probably my biggest garage draw at the moment and will eventually want a smaller welder. Can I run a 200A sub off of the house panel? Would a separate service to the shop be a better idea? It's going to be a 300ft run from the house panel and not much longer to run from the transformer itself for a new service...

 

[JMURiz]

From what I've been told (and what I did) was that you can run a 100 amp subpanel off of a 200 amp breaker box getting 200 amp service. Just make sure the wire from the main electrical grid feed (overhead or underground service wire) is large enough for that load and the line from your meter to the main pannel is large enough also. I also made sure to run #2 copper wire for the hots to the sub and #4 for the ground and neutral (I think those were the specs). That's some expensive wire so if you have a contact to get a price deal, use it!
Best of luck.

 

[PAToyota]

It is hard to make a general rule of thumb on this sort of thing. I wouldn't design a subpanel that took more than half the load of the main panel, but if the main panel is already "loaded" you could still get yourself in trouble. Add up what you already have that is a regular load - air conditioning, electric heat, lights, that sort of thing - and look at it that way.

What I did was start with a 200amp panel in the house and update the service to 400amp (what they call commercial 320 or C320 service) and then put a second 200amp panel in the workshop. The power comes in to the meter and then splits from the meter box to both the panels. Many places you cannot get two services to a residential property, so this is the "next best thing" to it.

 

[leadsled01]

I have no idea what the transformer capacity is. It is what PG&E refers to as a "Single Stand", and I am the only customer connected to the transformer. It is at the end of the line (the high-voltage lines stop here).

Usually there is a number on the transformer ie; 15,25,50... This is the KVA of the transformer. If you have a 5 KVA trans well that could be the problem. Alot of times its corrosion in a connection. Call the power company and have them check all connections. I'm a Lineman for the local Electric Dept been there done that!!!!!

 

[Rrumbler]

I sort'a think it's time for some serious upgrading, Will. I don't know how long your place has been in existence, but it used to be common "rule of thumb" practice to install a 3 or a 5KVA transformer and a #4 aluminum triplex service drop to a single 100 amp panel; sometimes, they even used #6 copper triplex. Since you have obvious voltage drop problems, an increase in your panel, and the PG&E service seems to be in order.

 

[redsled]

What I did was start with a 200amp panel in the house and update the service to 400amp (what they call commercial 320 or C320 service) and then put a second 200amp panel in the workshop.

That is what we issue at the EMC 320 amp and have them install two 200 amp panels on each side of the 320 meter box. My shop and what he has said he will use this would have been sufficient. Although as everyone knows you can't stop putting things in the shop to play with.

 

[Charles (in GA)]

I considered 400 amp to the house and split 200 off to the shop. Currently I have no outside disconnect on the house and three wire to the panelboard. To upgrade the building inspector was requiring an outside disconnect for the house and for the shop along with the 400 amp meter, all of which would have required a new underground feed to the house, and also 4 wire to a new panel with isolated netural and grounds, not worth the hassle, expense and being without power. I ran a feed from an unused transformer (was a 5 that ran a yard light, they upgraded to a 10) and a second meter on the shop. Minimum bill each mo on the shop is $14 and I use at least that much anyhow, so the meter charge is minimal to non-existance most months.

Two feeds from different power sources is nice, I lost the underground feed to the house and was able to run the fridge and a couple of lights using a 100 ft 12 gauge extension cord run from the shop, for a couple of days till the feed was repaired.

Charles

 

[wilbilt]

Well, I've had my Fluke 23 plugged in for the past couple of days monitoring voltage in the house.

Nominal is stable at 122.4 V. When the compressor is running, it drops to 116-117 V. That doesn't seem like a significant drop to me. I still need to measure the drop at the compressor breaker.

The general loads lately have been small. I don't have A/C, but the temps have been mild, so the swamp cooler isn't running. Hot water and cooking are propane. The other largest electrical load is the clothes dryer.

This place was first developed in 1973. I assume the transformer has been here ever since. I know it hasn't been touched since 1985. It seems like there was a number on it, although I assumed it was an ID number rather than a rating. It has since faded.