Help Required for Determining Elec. Load for Roof De-Icing Cables

Hey Capt,

Sorry to hear about your ice problems.

4000W / 120V = 33.33 Amps

4000W / 220V = 18.18 Amps

At 120V go with a 40A CB, 2 #10 and #12 Grnd

At 220V go with a 25A CB and 3 #12

NEC Article 310

Hope this helps - Good Luck

I hope this blizzard we are experiencing right now peters out before it gets your way Gotta keep going out to brush the snow off the satt dish or I lose my internet

Hey there KJK/USA,

Many thanks for the help! You're a life saver!!!!

Geeessshh, the comps are as simple as that? LOL My gray matter has turned to mush in regard to EE calcs.....been 27 years since my last Electrical Engineering course during my BSE college years. I suppose if you don't use it yo lose it! I really lost it BIGTIME and the electrical textbooks are safely tucked away in one of the large plastic tote boxes down in the basement...somewhere as there's a lot of them there unmarked from the last move.

Be safe and warm in this blizzard, especially clearing the snow and freezing rain off that antenna! We have the Dish Network for cable TV and I'm constantly clearing the snow off the antenna as well as the roof.....can't reach the antenna with my 28 foot long snow rake pole (chimney mounted) so I have resort to throwing snowballs at it! LMAO Ohhhh my aching arm and shoulder! I half expect to lose the signal any moment now since we're getting a heavy snowfall mixed with freezing rain now...about 3-4 inches per hour. YUKKKKKKK

Luckily, our Net is via the underground telephone lines here. Problem will be that the Grid will come crashing down on account of the freezing rain taking out the trees, power lines, and telephone lines. Thank goodness I have a standby 15 kW GenSet on auto switch just in case. It'll power up the entire house, and then some!

Again, thank you for your assistance KJK!

===CaptMoosie

If I may add, since your system is capable, it will be more advisable to go for a 220 volts system rather than 110 volt. Not only it will require a much smaller wire gauge and lower CB amperage, the 220 volt heating system will also add a balanced loading to the existing electrical system.

The ice on the roof is caused by the heat from the attic melting the snow in the upper section of the roof. The water then drains down to the lower part of the roof that is usually cooler and freezes. This produce ice jams and icicles. Adding heaters might help reduce the symptom but will not solve the problem.

It would be a better investment to add insulation in the attic and improve its ventilation. You would then save energy (summer and winter) in the next 20 years instead of spending it.

In Canada, we use R-40 as a minimum for ceilings and place large ventilation chimney to draw the warm air from the attic. Here are a few links:

http://www.joneakes.com/jons-fixit-database/1497

http://www.polarcentral.com/maxivent.htm

Trouble is that pesky sun hits the roof, and causes melt. But its true, that since I properly ventilated the attic, the ice dams are much less of a problem. Upstate NY and Southern Ontario (where I live) are pretty close together, and both get the most miserable wet snow imaginable. A drive through the countryside towards Potsdam will take you past several buildings which have collapsed due to ice build up. They get hit worse than Canada does! Go figure.

You are correct that the sun has something to do with it but when the roof is well ventilated, the melting only happens in the above freezing days where the ice doesn't form in the eaves. Unless a cold front comes rapidly, the day's melted show has time to drain (mostly) before freezing.

I used to own an old house that made icicles in the end of winter. I built my new home with good roof ventilation and insulation. This has eliminated the icicles where my neighbor's older home still have them. On my new house, only the eaves through fill with ice. I am planning to paint the inside black this summer to see if I will get enough thermal gain to keep them dry in the winter. I want to use passive solar heating...

This all to say that I understand how difficult it is to implement the real solution but it works.

The other contributor to ice buildup on the edge of the roof is heat escaping from windows (yes, even the newer thermal windows are still "holes in the wall" compared to real insulation!) and along the interface of the top of the wall stud plate and the rafters. There is often quite a lot of heat escaping at that junction, either by air leakage.

Unless the gas furnace vent exits the roof where the problem exists, as it does on my roof. All the attic insulation in the world will not stop the melting created by the gas furnace vent. I get a massive build up down roof from this problem.

Question for the Canadien - My local is not too different than yours, as the only thing between me and your country is a "great" big lake. I have given up on rain gutters because of 5 months of lake effect snow and below freezing weather. Do they still install them up there?

Yes. But I am not convinced that they are that useful when the house is on a hill with good drainage.

On flat surfaces or even worst when the yard slopes toward the house (actually a common problem), moving the water away from the foundation is important. Unfortunately, the gutters bring other problems...

I am still looking for a good way to clean them or prevent leaves accumulation.

Regards.

Hello All,

Thanks for the valuable insights guys.

Unfortunately, I can't get up into the attic like I wish I could because I need to lose some more weight and it's a tight fit up there getting through the 24" x 24" ceiling door. Then there's dealing with the wooden roof scissor-trusses spaced @ 24-inches o/c. As far as I can tell I only have roughly 4-inch depth of fiberglass batte insulation between the truss bottom chords. I have no idea of whats in the roof eaves. I suspect that there's probably very little insulation there in the eaves as they only extend out 18-inches from the exterior wall face and are approximately 4-inches deep. I desperately need to find a way into the attic or hire a Contractor to blow some more loose insulation into the attic space. BTW, this is a very well-built modular pre-fab house built in 1986. A new very high quality 30-year asphalt shingle roof was installed 3 years ago. We never had any previous ice dam problems until this Winter, but then again they were mostly mild winters with very little snow fall accumulations, unlike what we have experienced this Winter.

I do know that we have a very good continuously vented roof ridge and eave soffit vents, so air circulation is probably not the culprit. Snow and ice tend to stay on top of the roof for a very long time, even when we have sunny days. Lately we have been clobbered by a series of snow and snow/freezing rain storms the past 45 days or so....we just went through Winter storm #10. Where I cannot reach the upper reaches of the roof with my 24-foot long roof rake I have about 24-inches of standing alternating ice and storm layers. The bottom-most layer over most of the roof is a compacted layer of ice that's well-adhered to the new shingles, unless I was able to break it free with my high pressure power washer...max. pressure is around 1,750 psi. I have it hooked up to a 30-foot long telescoping fiberglass pole where the rubber hose runs up it's interior and is topped with a high pressure fan pattern brass nozzle (or other type sometimes). Ice and now removal has been tedious and somewhat ineffective, with the end result being that I get soaked to the bone even wearing my old water resistant US Army Artic gear. Plus I get frozen pretty quickly, especially my hands! ACCKKKKK!!!

Yusef, I think I know what building that you are describing up near Potsdam! I frequently have to drive up there as my 2nd daughter is currently attending SUNY at Potsdam.....I'm the Bus Service for her and her buddies!!! LOL It's a long long freaking drive from here (down in the Mid-Hudson River Valley). I personally feel that the Snow Load Map included in the New York State Building Code should be bumped up another 10 PSF, with no reduction permitted whatsoever in the superimposed design snow loads used for design roofs, especially for prefabricated wooden roofs. Over the past 34 years I've forensically investigated dozens of damaged and collapsed roofs, both for residences and commercial/business buildings.

FYI, this morning I posted a thread in this forum regarding the issue of leaking roofs and the need for new snow and ice removal technologies, with a corollary blurb busting on "Phil the Groundhog". Please check it out!

Keep warm and safe folks!

Perhaps he should look at salt, or some other chemical fix?

When you put on a roof, you should roll out a couple of layers of "ice and rain barrier" onto the plywood. It is a wide black rubber sheet, sticky on one side. It is required by code up here, but because it is "up there" out of sight, often they skip it. Beats tar paper all hollow. Then you have to put up shingles or steel on top of that.

You tell me you have fairly new shingles. So ripping out the shingles and nailing up the correct roof material may not be cost effective. (Heck, I put up steel right over top of my crappy old ashphalt shingles, and that roof will not leak while I am alive!) If you are getting leaks, the roofers did not install the ice and rain barrier. Personally, I don't trust the the heaters. They can fail on you when you most need them, and they are a continual drain on an increasingly fragile and overextended electrical grid. Mine were on there when I bought the place, and they quit working after about 5 years....weather will do that to electrical joints.

Oh, and your snow rake won't be useful once you have stuff up there....be it solar panels, or ice dam busters. My neighour dumped a bag of salt on it last winter. Fixed the problem, but killed all his wife's flowers.... grrr.

Anyway, just chatting...not really suggesting anything. Roofs are near and dear to my heart...I seem to be spending a fair amount of time up on roofs fixing problems that should not be there in the first place.

"I seem to be spending a fair amount of time up on roofs fixing problems that should not be there in the first place."

Is this the kind of time you spend on the roof?

http://www.youtube.com/watch?v=U9hbNeA_aH4

power=voltage x current [A]

the circuit braker shall be about 50% more

.

HEY YOU ARE NOT THAT BAD ,HOW DID YOU COME UP WITH 4000W IN THE FIRST PLACE

JS

Dear Guest,

To arrive at the 4,000 Watt figure I knew I needed no less than 800 linear feet of de-icing cables to cover all of the eaves and partial up the roof (serpentine pattern) + cable draped over the roof ridge vents (currently water is entering through them....backed up ice there too), + back and forth runs of cables in all of the rain gutters & gutter downspouts.

The de-icing cables I'm purchasing are rated at 5 Water per LF.

Total P = 800 L.F. * 5 W/L.F. = 4,000 W