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| Subject - 3 phase heater question ? | |
| shane |
this heater says on the wire diagram that it can be wired for 15-50kv 208,240,480,vac 60hz, 3 or 4 wire power supply. And it shows the typical wire diagram for such, but, as everyone knows 3 phase is non-exsitant for most folks. i wolud like to rewire it to single phase, my question is about the heating elements. at the moment they are wired like this  and i want to keep the amps as close as i can to keep from burning them out. how many amps are they running at now at 240v 3 phase per element? and right now it seems to me they are all ganged up..? so how many elements on one breaker, and what size amp breaker, for 240v single phase ? any help on this would be greatly appreciated. |
| wareagle | Shane I see why you are not getting responses. This is got to be the worst wiring dwg I seen. What is the wattage of each element? Voltage? In your first sentence is that supposed to read 15-50 kw? What do the pink lines mean? It appears pink is shorting the blue-green, orange-blue. |
| JimmyDee | quote: Here is my take on this "worst dwg". It appears like it is wired 3 phase with the green and yellow being used as jumpers. I just spent 15 min on this abortion and realized the contactor has to be a multiple position and unless we know the configuration of switching, the diagram will do exactly what it is doing. Make no sense. Looks like they are doing a changing of series and parallel wiring with the contactor??????? Jim |
| shane | sorry for the bad diagram but i had to physically make it with a photo editer the pink represents copper bars. and all wires are actually black and yes 15-50 kw where did that v come from... i been looking at it some more and ... single phase 240 is wrong too... id like to use 220 like a kicthen stove... |
| JimmyDee | 220 - 240 volts is considered nominal voltage and for all intents and purposes, is the same. Can you scan the diagram that came with it? Jim |
| JimmyDee | OK I've got it figured out. With the copper bars, you are paralleling 3 individual 240 volt elements. When you series 2 of these units together, you can apply 480. I'll work on a diagram for you but you need to realize that 50kw of heat powered by 240 single phase will draw 208 amps. Thats a good size feed for heaters. It looks to me like the contactor is cutting half of the heaters or more to cut the KWs of heat. Need to know how that is set up and working. Are you sure you need all 50KW of that heat? Thats 170 BTUs and is equivalent to a 200,000 BTU furnace at 85% efficiency. You could heat a huge home in Michigan with that. Mine is 1600 sq ft and I'm using a 75,000 BTU at 85%. I would think you could easily do a well insulated 5000 sq ft home with that much heat. Do you realize that, depending where you are located, this unit is going to cost you between $6 an $7 an hour to operate? You may need to get an OK from the power company to hook this up as well. Jim |
| shane | heres a wire diagram that was in the box but its not quite the same as whats in the box http://home.earthlink.net/~srstrs/sitebuildercontent/sitebuilderpictures/wire.gif it dosent have to be that hardcore but we want to use it in a shop that might get used twice a week for a couple hours a day so id like it to heat up quick because if nobodys in there it wont be on. the shop is 1200 sq ft. wow thats alot of heat.. i got it from an old k-mart store oh did i mention i have two of these.. i can change out the fan motor if necessary and i only have a 200 amp service... so probably need to drop some of the elements ive already had to have the transformer on the pole replaced due to overloading ...doubt the electric company would like to do it again.... |
| JimmyDee | You could probably start by eliminating half of them. Maybe, since everything is there, we can figure out how to wire it by using 1/4 of the elements for stage 1 and 1/2 of them for stage 2. Don't forget that the heat from these is 100% there. No inefficiencies due to the flue gasses etc. Hope you don't need this tomorrow. Will be doing Christmas stuff for the rest of the day and tomorrow. Jim |
| wareagle | Shane I would suggest that you get the heaters down to 15 or 20 kw. A shop that size won't require much. I would split the load in 2 parts, 2 7.5 kw or 2 10 kw if thats possible. This will allow you to have the heat stagged so that the first 10 kw is on and if needed the 2nd 10 kw would come on if required. Sorry about the critizing of the drawing. Bob |
| JimmyDee | L1 L2 |--------| |--------| |--------| |--------| |--------| |--------| |--------| |--------| |--------| Using half the elements rewired like this will give you 240 volts, single phase, 25 KW of heat. Vertical bars are continuous. For each element you add or subtract from this, you will add or subtract 2.8 KW or 11.8 amps from the load. Which ever 2 contacts you choose to use for the line in use the same corresponding load lugs and you should be making heat. Jim |
| shane | Thanks...probably play with it tomorrow.. |
| shane | ok, im a little cofuzed here... I looked in my panel and found a 220 double pole breaker rated at 40 amp for each side...so I wire up 3 elements L1-------L2 |---------| |---------| accoring to the math this should be 8.4kw and 35.4 amps just to check that the elements were working and they did. let it run for 10 min, not much heat ... so I then added another element this should change it to 11.2 kw and 47.2 amps expecting it to trip the breaker ...it didn't.. then I added another element as I figured 7.2 amps overload might not be enough to trip the breaker.. so now there are 5 elements pulling 14 kw and 59 amps and it still didn't trip the breaker... so I thought faulty breaker and change it out with another 220 double pole 40 amps per pole breaker. and no differance..... am I looking at this wrong... |
| JimmyDee | You are looking at the dashed horizontal lines as a complete element, right? Jim |
| shane | yes and ..since then... I'm up to 7 elements, still havent triped the breaker. they now heat up in about 5 min and the meter turns 1 kw in about 2 min. at the moment I have it wired straight to the circuit meaning no contacts and no fan motor. my wiring is 10-2 about 8 ft long. I don't let it run longer than 10 min. I figured the circuit would trip much sooner than this. .... (meter might turn faster because it's an old 4 digit one from a 80 amp service. the co-op sold me one when I ran a business out of the shop, so I could deduct the kw on my taxes. it's wired through a 200 amp service that runs the whole property. didn't we used to add a zero when we read the older ones? does that make it 10 kw ?) .... |
| JimmyDee | Well, 1 KWH in 2 min would be about 30 KWH in an hour so I'm thinking you are in the ball park with 7 elements. Would be closer with 9 in there. Its possible the elements are 480 but they should be 240 for the duel voltage set up. I think you need to borrow a clamp on meter to read the amperage and double check the voltage to see if it is close to 240 instead of 220. Don't know what to tell you about the breaker. I agree, it should trip. I don't think these elements are made to get red hot because they have air flowing over them all the time |
| wareagle | Shane That load may take 10 or 15 minutes to trip the breaker. If you had the trip curves you would see the time require to trip. This is not a short circuit so the breaker does not trip just because the load exceeds the 40 amp rating. Edit Addition I looked at the curve for a Sq D 40 amp and it should trip after 150 sec with the load you listed. I was a tad off on my estimate. |
| shane | I go back to work on the 3rd, I can borrow an amp clamp from maintenance. I'll let ya know what find out... |
| shane | amp clamp results: for each element 2.6 - 2.3 amps with all elements and fan about 50 amps on 220v and meter on the pole spins at about 45 - 50 kwh thats going to run about 35.00$ hr, ....humm....propane ? |
| JimmyDee | I thought this might end up like this. Not sure about the propane but they may make a vent less heater that could work out good for you to use as a temporary heater. I have a natural gas one that I use as an emergency backup unit that works great. Jim |