70 amp service

uhmgawa · Jun 19, 2003

( I was wondering, how far can you take the electricty after it has went through the transformer. )

Another issue is to verify the transformer supplied is
sufficient for your service. I have seen undersized
transformers supplied to new installations with the
rationale of upgrading to a higher KW unit if and when
the demand exists. On the other hand the step-down
transformers are typically designed to handle double of
rated capacity on a fractional duty basis.

uhmgawa · Jun 19, 2003

( Now for the good news...a 200 amp feeder shouldn't really care about that extra 50'. Go for an extra 250' and you'll need to start looking at the size of the wire to minimize the voltage drop.)

The rule of thumb is to keep total voltage drop under 5%.
This includes everything from the transformer to the load
(service lateral, sub panel feeds, breaker-to-outlet).
If you consume too much of the voltage drop budget in the
lateral, you may have to deal with the issue multiple times
downstream.

Anonymous Poster · Jun 19, 2003

/forums/images/graemlins/tongue.gif Reading through the list of postings to your original query, I can see lots of good advice offered here. /forums/images/graemlins/smile.gif After looking through the lens of an infrared camera for almost thirteen years now, i can tell you that I have seen VERY FEW shop electrical feeds that were overloaded. Yes, there IS a lot of connected load in shops, but the reality is that they are rarely used altogether, so even a 100-AMP dedicated shop service goes quite a ways. /forums/images/graemlins/tongue.gif When we re-wired our 100-year old Iowa farmhouse this last year or so I knew we'd have a shop to feed eventually so I asked for a 200 AMP service. The power company installed a 15KW transformer which is what they consider a 200 AMP service and in actuality it is only 125 AMPS at nameplate rating (AMPs X Volts = Watts). The drop to the main is also way undersized from what I have popping out of the building; mine was 2/0, their cable is #1 AWG. Power companies depend on the OUTDOORS to cool their stuff, so they fudge quite a bit on everything, /forums/images/graemlins/frown.gif whereas our stuff which is all in conduit has to be sized by the book. /forums/images/graemlins/tongue.gif It isn't unusual for the power company to load transformers to 1.3 times nameplate, and that's continuous use. /forums/images/graemlins/tongue.gif We used a 200 AMP DISTRIBUTION PANEL which is just that, a distributor to sub panels. The distribution panel has a 200 AMP main, and four breakers below that which feed two 100 AMP subpanels, and two fifty AMP subpanels. BGOTT's idea of using a pass-through panel and connecting to the bottom is good because it avoids taking serious power off some teensy little push-on breaker connection. it does, however, mean that your feeders beyond that point would need to be 200 AMP rated, all the way to the second panel, whereas our setup with a genuine distribution panel made for that job allows for the distribution breakers to be right there for us to use. I'm a believer in the MAIN/DISTRIBUTION-to-SUBPANEL approach, but then I do my own stuff and that does make a difference in costs, no doubt about it. /forums/images/graemlins/tongue.gif

uhmgawa · Jun 19, 2003

( The power company installed a 15KW transformer which is what they consider a 200 AMP service and in actuality it is only 125 AMPS at nameplate rating (AMPs X Volts = Watts).)

15KW: 125A @ 120V or 62.5A @ 240V. An electric Kitchen range
weighs in worst case just under 50A/240V and an electric water
heater just under 30A/240V. So we have already exceeded the
stated rating of the transformer and I haven't even fired
up the welder.

From this it would be reasonable to assume there is
sufficient thermal mass in the transformer and cooling oil
to absorb large short-lived excess draws and enough
surface-to-air cooling to withstand longer, more modest
overloads.

Aside from the voltage drop associated with exceeding the
transformer design limit, somebody is paying to heat the
works up there on the pole. Be happy it is on the utility
company's side of the meter.

I'd suspect the rating of the transformer is that which may
be drawn at an acceptable efficiency (read: cost) to the
utility company.

tc35dforme · Jun 20, 2003

Short of going too far on electrical theory...transformers are most often ( always ) rated in VA or KVA which take the voltage and amperage into consideration. Three phase gets a little weird by factoring in the square root of 3 ( 1.73 ).

I have a 25KVA padmount along my driveway placed by the power company on an underground 7.8KV ( 7800 Volts ) feeder. It good to have some connections /forums/images/graemlins/cool.gif.

Anonymous Poster · Jun 20, 2003

Actually, the power company claims 125A PER LEG at nameplate rating on that 15KW transformer. /forums/images/graemlins/tongue.gif These transformers are really strange since I'm not used to seeing a single leg of 7800 volts going into a transformer and TWO coming out at 240 volts. /forums/images/graemlins/crazy.gif Out on the west coast we always had one primary for each secondary on both single AND three phase. We don't have an electric range, but we do have an electric water heater and air conditioning, plus an electric dryer. If we did have an electric range, I estimate that I could run the whole works and still be able to weld in our shop. The power company definitely does take some liberties with the service factor on these pole-mounted transformers, but they must get away with it as evidenced by the very infrequent outages. I have no doubt that if I had everything electric and on all at once that there would be a definite voltage drop on the overhead service drop since it is the observed bottleneck in our entire system. In that case I would simply get a hold of the crew foreman over at the power company, and have them upgrade the drop to 1/0 or even 2/0 wire. /forums/images/graemlins/tongue.gif In actual measurement, we have 12 AMPs to the A/C condenser with an additional 6 AMPs to the circulator fan; 22 AMPs to the electric dryer on high heat; the water heater pulls about 24 AMPs. The TV pulls about 3 AMPs and miscellaneous lighting and kitchen stuff that cycles on-off adds another 9 or 10 AMPs. The HOUSE itself can get by nicely on a 100 AMP service as it is, but with an electric range, it would be crowding things a little; doable, but it would take some management. With a 200AMP service we end up with a good margin for the shop, even if we did have an electric range. 400 AMP services are not unusual if the house has zone A/C like they use out out west and maybe double ovens. The last month we were in CA our household electricity cost $343.00....that was in August with lots of A/C running.

Anonymous Poster · Jun 20, 2003

( The last month we were in CA our household electricity cost $343.00....that was in August with lots of A/C running. )

Ouch! /forums/images/graemlins/shocked.gif

SnowRidge

Anonymous Poster · Jun 22, 2003

/forums/images/graemlins/tongue.gif And that was with power outages in a rotating-block sequence.....YUK! It was just ONE of fourteen good reasons that we put together to get OUT of California. /forums/images/graemlins/frown.gif The year 2001 was all about GENERATORS! /forums/images/graemlins/tongue.gif

Anonymous Poster · Jun 23, 2003

Wow. I run a 200 acre farm (35 head of cattle, electric deep well, electric stove/oven, electric water heater, 1 window air conditioner, welder, assortment of power tools & small grain augers, etc.) and the entire place has a 60 amp service. Bill is $35-40 most every month. Coop power in southern MN is pretty good. Do wish I had a 200 amp feed & could branch to the outbuildings a little better.

--->Paul

Gary_in_Indiana · Jun 23, 2003

I know it's done. It would just make me nervous doing it with my investment and my personal belongings. I don't know a whole bunch about electricity but I think if I knew more I'd be more nervous about it than I am already. I do know that the vast, vast majority of residential fires in the US every year are electrical in origin. Maybe that's a part of it. /forums/images/graemlins/crazy.gif

Here's hoping your luck continues. /forums/images/graemlins/smile.gif