Let the record show that Gunner Asch wrote back on Tue, 13 Sep 2005 05:21:52 GMT in rec.crafts.metalworking :
So, like, you're saying I should let my brother-in-law make any adjustments?
When I was younger, I lived in Madrid, and in the new apartment, we were getting a step-down transformer installed to convert the local (220 volts) to American appliance (110 VAC). Heard the "zot" and kind of saw the flash of the short, definitely saw the electrician fall on his butt from the shock. He wasn't too hurt, but he utter those immortal words to live by: "I didn't think that was going to work."
Wouldn't it also be a factor that 120 volts is much more commonly available (and especially around those without much knowledge of electricity) than 480 volts?
Since I'm posting on the subject of 3 phase power from the utility co. I'm curious if 3 phase power is more or less expensive per kilowatt hour than single phase. Is it even a valid comparison?
Actually, the open circuit voltage in arc welders is about 80V, and the voltage at sustainable arc is about 25V, iirc. There is no strict magic number, because arcing ability is highly dependent on geomety, w/ sharp points arcing much more easily than flat surfaces--ie, higher electric field intensity at cusps.
The salient point is, the higher the voltage, the more arcing you can have.
If you're going to throw in the upstream safety devices w/ 440, you're changing the game. Majority of electrocutions at 120V?? Mebbe cuz 300,000,000 people have 120V wall outlets??
*Per capita*, proly by far the greatest number of electrocuti>
I've seen the term "demand metering" mentioned here several times and have gleaned that it can be expensive for some reason. What is demand metering and why is it more expensive than other types of metering?
(My dream is to sell my house when I retire and live in a shop which will have 3 phase power from the util. co.)
"Pax Americana is a philosophy. Hardly an empire. Making sure other people play nice and dont kill each other (and us) off in job lots is hardly empire building, particularly when you give them self determination under "play nice" rules.
Think of it as having your older brother knock the shit out of you for torturing the cat." Gunner
As I understand it, the meter monitors the sustained gross current drawn for a given period of time. If you go over a prescribed amperage (here, it's
50 kw), you are charged a higher amount for all of your consumption for that billing period. You must sustain the draw for something like 15 minutes in order to set the meter, so simply starting a large motor, for example, doesn't reset the meter. Because I don't have my induction furnace in operation yet (it's a 50 kw unit itself), I haven't come close to exceeding the demand.
The short-term reason is to reduce peaks so that the utility doesn't have to bring another generator on line or buy power from another utility.
The long-term reason is so that the utility doesn't have to make capital investments in lines and plant that will only be used a couple of hours a day.
The utilities have taken it a step further in some areas. They will give certain industrial customers a discount on all their power if they agree to cut their load upon request.
The meter will measure the peak current drawn from the line. Over a certain peak current you pay a demand rate in addition to the actual usage. The demand billing is to pay for the extra reserve and the cost of maintaining the larger feeder systems used to supply you the higher peak current. The electric company has a formula for calculating the demand rate. Every company is different in their calculations, but in any event you do not want to start too many motors at the same time.
The idle current form a small transformer that you run one machine off will not be that bad . My problem is that I needed/wanted to have 200 amps of power on the lower voltage (120/208) in my case derived from my single 600 amp 480/277 feed. since it's on my side of the meter it's covered by the NEC and that requires a 75kva transformer for the 200 amps even though I will NEVER pull 200 amps through it! In fact the Utility co feeds the whole
600 amp service with 3, 25kva cans on the pole ( at my request they will replace them with larger ones if I want/need them but they charge a min fee based on the size of the cans so the smaller ones work for me!)
My system is all demand metered ( and only one bill that way) BUT, at the magic "75kva average over a 15 min interval " they kick in the demand charge ( if during the 3 summer / 3 winter peak months) You can BET I will never let that happen as it's CHA CHING!! if it does. At almost $15.00 per KVA + the KW charge for the whole month. The 75 kva is a lot of power though and I don't think I will exceed that.
I wanted the wye and the 277 volts for the HID lighting is great. The cost of Cu wire is out of sight and I can run most of my machines off 12 gauge wire if I want. I only have 2 machines that didn't like the 480 volts, and one runs fine on the 208 and the other (the blade welder for the band saw) would have probably worked ok but I picked up a single phase 480volt to 240 volt transformer for cheep for the times I have to use that unit.
That makes sense to me. It's absurd to assume that the voltage makes no difference. Given a high enough voltage, an arc can generate when there are no proper conductors in the path. After all, aren't most insulators, for the most part, simply not good conductors? With enough pressure (voltage) anything will conduct------even glass. That being the case, it stands to reason that as the voltage is lowered, so is the propensity for arcing.
Martin Martin Eastburn @ home at Lions' Lair with our computer lionslair at consolidated dot net NRA LOH, NRA Life NRA Second Amendment Task Force Charter Founder
It depends entirely on your rate schedule. Either could be cheaper. I have two services, I pay significantly less per kwh for one, than I do for the other, even though both are 120/240 100A services.
If you have any 480V loads to run and you can get a 480V 3Ph feed from the utility without a hassle or a huge price penalty compared to
240V 3Ph, it's always far simpler to drop a 480V feed down to 240V for most of your loads with a cheap used transformer than it is to boost a
240V feed up to 480V.
And a 200A @ 480V feed goes a whole lot further. But as has been pointed out, 480V demands some serious respect because it will reach out and bite you hard, and things tend to "blow up reel gud" ;-) with very little provocation.
You put in the 480V meter section and main, a small (12 or 18 position) 480V distribution breaker panel to feed any machines that must be run at 480V, or fused safety switches - and be sure to run it in as 4-wire with a neutral in case you ever need 277V for lights. Then you install your 480V-240V transformer, and a larger (and much cheaper) 240V 3Ph panel for the bulk of your equipment.
If you want to run 277V lighting in a large shop, pay a bit more for the light fixtures with individual fuses inside. Without them, one ballast in a long string of lights goes bad and grounds out, and you go nuts opening every single stupid fixture to find the culprit. Or you split the circuit and test, and hope the circuit breaker lives through the repeated short-circuit torture test. BT, DT...
Run a separate "lights and plugs" feed out to the shop building from your house's 120-240V 1Ph panel feed, or leave the existing one hooked up. This way, you can kill all the shop power at the 3Ph Main to work on it, or just to kill the parasitic loads from the transformers and keep "unauthorized personnel" from messing with your toys, and not be in the dark.
With that power coming in on a totally separate feeder you keep the motor start surges and welder spikes away from the more sensitive gear. And no lights dimming when you hit the big switches.
Also, see mentions of demand metering and higher rates for 'commercial power' mentioned elsewhere - that way the lights, furnace blower, computers, clocks, and other incidental loads that tend to add up fast are being metered at the residential rate.
Consider getting three buck-boost transformers to drop a 240V or
208V line to 200V, depending on the price it's probably cheaper than a new motor. And you can use some ridiculously small and cheap transformers for that, even when buying new.
A lot of equipment does both 208V and 240V, the current is slightly higher at 208V. Makes it easier to wire up small industrial parks at
208V without people constantly making "Oopsies" hooking up 120V stuff to the ~190V 'High Leg' of a 120/240V Delta service.
If I had my way, ALL houses would be able to get either 120/208V Wye or 120/240V Delta feeds on demand - Just putting the largest motor loads like air conditioning/heat pump compressors on 3-phase increases the energy efficiency enough to make for a short payback period.
You dont' mention if this is an additional service or a replacement service. I had three phase installed a few years ago. It was a replacement service. I went with 240V center tapped delta. It's the way to go in my opionion. It will maintain all of your single phase service with no(minimal) changes. You will gain "true" three phase. Yes, there is a wild leg that needs to be kept in mind when considering single phase loads. It's not really a big deal.
Check with your power provider. They will have a PE on staff that can answer any questions. They can tell you what they will do, and what expense it may be to you. Going to 240V 3ph cost me nothing for installation. 208 or 480 would have been a minimal fee, but would have required other "local" infrastructure changes to accomodate.
As many have suggested, stay away from 480V power. It steps things up to a realm where you NEED to know exactly what you are doing or you will hurt/kill yourself/others. It will also increase the expense of equipment/materials. Everything will need to be 600V rated.
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