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Using two fuses to create double-pole for 240v

Posted by fasola-shapenote (My Page) on
Mon, Jul 5, 10 at 23:49

Hi all -

My house still has a fuse box. It's got two main pull-outs: 1 for the main cut-off, 1 for a major appliance (stove, in my case). It then has ten screw-in Edison-base fuses for the 110v circuits, three of which are unused.

I am adding an electric hot water heater (been using a non-electric range boiler until now), and need to wire in a 220v circuit. Can I use two of the unused screw-in 110v spaces - one for each of the hot legs - to accomplish what a double-pole breaker does in a circuit breaker box?

Also, what happens if only one of the fuses blows?

Thanks!


Follow-Up Postings:

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RE: Using two fuses to create double-pole for 240v

Once upon a time, in the Land With Many Fires, the approach you propose was commonplace. And, yes, it will work in the sense that the HWH will probably heat water so long as the two fuses are on opposite poles.

But is this up to or even close to modern code? No. Is it really a safe approach? Nope. Is it a good idea? Not likely.

"Also, what happens if only one of the fuses blows?"

Bingo! That's a good starting point. If one fuse blows, there's still a hot feed to the circuit and that's a big difference between this approach and "what a double-pole breaker does in a circuit breaker box." (A double-pole breaker ensures that both hot legs are disconnected when an overcurrent condition is detected.)

But the plot thickens:

From your description of your fuse box, I'd hazard a guess that this is an old 60-amp service. But even if the POCO is feeding you, say, 100 amps, the cable to the box is very likely #6 gauge SE with frayed cloth sheathing and the box itself probably had a capacity for handling 60 amps at low temperature ratings (e.g., 60C).

If these assumptions are more or less correct, you'll be adding a 30-amp HWH to box serving a 40-amp range circuit PLUS the load of those 7 other circuits. Go figure! If you add a HWH, you'll almost surely overload your sevice.

I'm sure you don't want to hear this, but it's time for you to upgrade to a modern main panel. IMHO.


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RE: Using two fuses to create double-pole for 240v

If only one fuse blows the water heater shuts off. However there is still live power at the heater that could kill you if touch the arong parts.

The stove block usually takes cartridge fuses. For lower amp devices there was a double socket that could hold two screw in fuses that plugged into the fuse box. Other than the double socket your plan is no different than how it was done for many years. Best to try and use two fuses beside each other for the pairing, just for clarity of where both fuses are.


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RE: Using two fuses to create double-pole for 240v

I believe it is now required, or at least a really good idea, to have a disconnect that will open both poles at the same time. This is accomplished with either a double-pole breaker, a fuse block box (with two cartrige fuses) or a two pole knife switch box (with two screw-in fuses).
A service panel upgrade would be my preferred route to take.
JMHO


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RE: Using two fuses to create double-pole for 240v

Hi all - thanks for the replies so far.

This is a 100-amp box.

If it makes any difference, it's a General Switch Co., Catalog #66110 - It says "AMPS 100, VOLTS 120-240 A.C., POLES 3 (S.N.)" on the sticker inside the door - It is identical to the one in the photo linked below, except that mine has a third row of two plug fuses at the bottom, whereas the one in the photo only has two such rows.

The wiring is all grounded Romex-style wiring, in excellent condition.

So I'm not concerned about replacing the fuse box, or overloading, or anything like that.

All I really want to know is whether or not I'm correct that, back in the days when everyone had a fuse box instead of circuit breakers, it was standard practice (i.e. code) to use two adjacent 110v screw-in Edison-base fuses to create a double-pole 220v circuit for things like hot water heaters, clothes dryers, central HVAC units, etc., once their one double-pole cartridge-fuse pull-block was taken up by the stove.

Thanks!

Here is a link that might be useful: Photo of very similar fuse box


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RE: Using two fuses to create double-pole for 240v

I don't know what the code said back then, but the method you describe is no doubt still being used many times a day.


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RE: Using two fuses to create double-pole for 240v

so just run the water heater on 120v..the wattage will be 1/4 of the rating..so the heat recovery rate will be slower.
the setup will be safe. and you save money heating water.

-dkenny


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RE: Using two fuses to create double-pole for 240v

(A) No thanks, I will be running the water heater on 220v.

(B) The consensus seems to be that the thing to do is to use two of the unused 120v screw-in plug fuse slots, preferably on opposite sides of the panel, so that they won't be on the same pole. As I understand it, I have two 120v poles (two 120v wires) coming in from the power company, and it would be best to spread the load equally to both of them. I would really appreciate hearing concrete confirmation on this from you electricians.

(C) One more question: since this is a 4500w water heater, I need a 30-amp circuit. Does this mean I use two 15-amp fuses, or two 30-amp fuses? And, please explain why, because I really don't get this concept.

The main pull block of the fuse box contains two 60-amp cartridge fuses. Does this mean that I'm getting 60 amps of power (under-rated for a 100-amp box), or 120 amps of power (over-rated for a 100-amp box)? Should I be using two 50-amp cartridge fuses, or two 100-amp cartridge fuses?

Thanks!


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RE: Using two fuses to create double-pole for 240v

(A) in all probability you will run your heater on "240 volts" -220 went away a long time ago. If you have "120" volts in a typical residential setting you have "240" volt across the phase.

(B)There is no "preferably" to this. If you intend to hook the heater to two fuses for 240V, it will not work if said fuses are on the same side of the phase.

(C) 30A. The short answer is because you do.

Your main fuses could be smaller because the rest of the service is good for only 60A, or they could be smaller because 60a fuses were what was handy one night when the main fuse(s) blew. The former combined with 100A fuses may buy you a first class ticket into the "land of many fires".

I respectfully submit that the questions you ask indicate that you have a real need for the services of an electrician, as opposed to advice from this board which is generally useful to those with a more complete grasp of electrical practice and theory.


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RE: Using two fuses to create double-pole for 240v

From your description of the panel it is a 3 phase panel ( POLES 3 ). That panel does not belong in your house.


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RE: Using two fuses to create double-pole for 240v

The purpose of using two different poles for your power source is not to "share the load", as you put it, but it is done this way to obtain a 240v voltage potential between the two leads to the water heater. If they originate from the same pole, you have NO voltage.
You'll need to either test with a voltage meter or know the internal connections of the panel in order to ensure you'll have the desired output.


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RE: Using two fuses to create double-pole for 240v

"From your description of the panel it is a 3 phase panel ( POLES 3 )."

If the picture above is similar, it is a regular 120/240 V fuse panel.
The cartridge carriers all appear two fuses wide.

In a 3-phase fuse panel the carriers held three fuses and were almost square, not rectangular.

You should up grade the whole mess.
You are likely running on very borrowed time even know.

The old insulation is probably so brittle the slightest movement will make it fall off the wires (like trying to work in the box to add another circuit).


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RE: Using two fuses to create double-pole for 240v

I'm not sure what in the description lends you to believe there is 3 phase power here.

A 15A fuse on each 120V leg makes a 15A at 240V circuit.
Do not increase the sizes of the fuses without changing the wiring! That's illegal and unsafe.

Make sure that there is NOTHING else connected to the fuses you intend to use for this. First, you don't want to have 14g wires live with your 30A fuse. Second, you don't want any 120V loads with this suicide connection arrangement.

The "consensus" is to do it properly which most likely would be advised to replace the mess as Brick says.


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RE: Using two fuses to create double-pole for 240v

Okay, with the water-heater issue out of the way, I've still got one pressing question:

This is a 100-amp box, with a 100-amp service coming to it from the power company. Should I have two 50-amp cartridge fuses, or two 100-amp cartridge fuses? Seems to me it should be two 50-amp fuses...50 amps on one pole, 50 amps on the second pole, is a 100-amp set-up, right? If I were drawing 50 amps between one pole and the neutral/ground, and 50 amps between the other pole and the neutral/ground, I'd be getting my full 100 amps, no? Seems to me to be the only logical thing also, because the main pull-out block uses ferrule-end fuses, not knife-blade-end fuses, and since all 100-amp cartridge fuses are knife-blade-end, and since the manufacturer's sticker clearly states this is a 100-amp box, nothing else would make sense.

And, for the record, this is not a three-phase box. This is a standard old-fashioned single-phase 120v/240v residential fuse box.


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RE: Using two fuses to create double-pole for 240v

http://www.inspectapedia.com/electric/ElecAmps.htm

N.B.
common defect found in upgrades of older equipment is the installation of a new 100-Amp panel and main breaker while failing to replace the old 60-amp service entry cables. This is either incomplete work or work by an untrained person. Keep in mind that by service entry cables we're referring to the cables from the mast head (point of attachment of overhead wires to the building) down to the meter and from meter into the main switch or panel. Overhead wires, being cooled by open air, may be of a smaller diameter determined to be safe by the utility company for open air use.


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RE: Using two fuses to create double-pole for 240v

".50 amps on one pole, 50 amps on the second pole, is a 100-amp set-up, right? "

NOT right.

A 100 amp service delivers 100 amps at 240 V.

The rating of the box does not determine the service, though it can limit the service capacity.

A box with a higher rating can be used on anything less than its rating.

The entire feed from the POCO overhead lines to the box determines the size of the feed.

Conductor size, insulation ratings on conductors, meter contact ratings, meter capacity, etc. all come into play.

The POCO should be able to tell you what they believe they are delivering.

You can go up to that capacity, but not over.

This is such old equipment I would be very nervous about trying to increase its load capacity.

I have pulled many old feed lines from conduit that had the insulation simply fall off the wire.

The fireworks from a failure before a main panel are often rather spectacular.
The POCO can deliver things like 10,000 amps.

Metal conduit can have holes blown in it from the arc.


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RE: Using two fuses to create double-pole for 240v

Yes, I forgot to suggest calling the POCO. If you decide to plug in bigger fuses without careful consideration, please make some clips of the results in real time. I like fireworks!


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RE: Using two fuses to create double-pole for 240v

As previously stated:

* The fuse box is rated for 100 amps

* The service - according to Progress Energy, my POCO here in North Carolina - is 100 amps

* All of the house's wiring has been replaced within the last three years - it's all modern Romex/Loomex stuff, properly installed, grounded, and in perfect condition

* The meter, meter box, masthead, and POCO leads have all been replaced within the last ten years

- - -

The only thing I'm still looking for input on is about the main pullout fuses; please address this:

"This is a 100-amp box, with a 100-amp service coming to it from the power company. Should I have two 50-amp cartridge fuses, or two 100-amp cartridge fuses?

Seems to me it should be two 50-amp fuses...if I were drawing 50 amps between one pole and the neutral/ground, and 50 amps between the other pole and the neutral/ground, I'd be getting my full 100 amps, no?

Seems to me to be the only logical thing also, because the main pull-out block uses ferrule-end fuses, not knife-blade-end fuses, and since all 100-amp cartridge fuses are knife-blade-end, and since the manufacturer's sticker clearly states this is a 100-amp box, nothing else would make sense."

Thank you.


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RE: Using two fuses to create double-pole for 240v

Some of those older boxes fed the range circuit from the line side of the "main" fuses. Ranges were typically 40A back then, combined with 60A in your "main"-there is your 100A 240V service.

Once again-I respectfully submit that the questions you ask indicate a need for the services of an electrician, as opposed to advice from this board which is generally useful to those with a more complete grasp of electrical practice and theory.


Now-I'm done.


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RE: Using two fuses to create double-pole for 240v

As said by Wayne and probably others above. The cartridge fuses are only protecting the smaller fuses for the lighting circuits (basically the lighting main) When you pull the main fuses out, the stove circuit still has power, it has its own main basically (the other pull out cartridge) Typically the bus is rated for 60 amps which is why it does not hold knife blade fuses. 60 amps for lighting side and 40 or 50 amps for the stove circuit. It might even add up to 110 amps, it was determined OK with a load calculation. 100 amps would mean 2 100 amp fuses, that is 100 amps at 240 volts. Not 100x2 = 200 amps, that is not the way it works. 200 amp 240 volt service would have 2 200 amp fuses or breakers. It is a 100 amp box because of how it is split to the stove and the lighting fuses. Even primitive breaker panels did this for a while. 100 amps coming in with 6 different breaker handles serving as mains. One for A/C, one for dryer, one for stove, one for all the smaller breakers (lighting). Adding up the breakers would usually be above 100 amps but it was allowed and just an old way of doings things. Code allows up to six throws for the main shut off and the service size was determined by calculation (not just adding up those 6 breakers)

Your true service size would be determined by the conductor size coming in and the rating of the meter. It is possible that you have a 60 amp service feeding that 100 amp panel (find this all the time) It works but is dangerous. If you brought the panel to near 100 amps of use, It would be a fire hazard with the undersized wire coming in. This would be easy to do with both the water heater and stove at the same time in combination with other household use.

Your on thin ice trying to rig new items to the panel. Your 2 30 amp fuses serving the water heater (likely using about 22 amps per leg) Will be sharing that 60 amp lighting main. Put that in combination with the microwave, hair dryer, and general use items in the house and you'll be dealing with blowing that 60 amp fuse often.


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RE: Using two fuses to create double-pole for 240v

Without examining the old box to see how it is built and wire internally no one can safely tell you how to proceed.

It really is electrician time.

Either to determine how the old equipment is built, or to upgrade it to circuit breakers.

A 100 amp main panel is not very expensive.

I have seen more kludged up setups with old fuse panels than you would believe.

One house I renovated had a 50 amp meter that was clearly labeled right n the face of the meter.

The feed from meter to the first fuse panel was in rigid conduit (beside a driveway) and the cloth covered rubber insulation was cooked to a nice crispness.

There were 5 or 6 seperate fuse boxes scattered on the wall.

The overall main was a lone plug in cartridge fuse block with 100 amp fuses installed, feeding all the other stuff.

There comes a time when it is simply more cost effective (and far safer) to remove the old stuff and put in a new panel.


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RE: Using two fuses to create double-pole for 240v

Okay I only read about half of the existing posts before my eyes started getting heavy.

I don't know if using two plug fuses right in the main box to get 240 was ever "common" but I've never personally seen it.

What I've always seen, where fuses were used, was a seperate fused disconnect, containing the two fuses (30A in this case), wired back to the "SUBPANEL" terminals inside the main box.

The most common application of this around here is adding electric dryers to the 4+range boxes used in some of the older apartment buildings. When this is done, most commonly a 2-space QO breaker box is used with a proper double-pole breaker, still connected to the SUBPANEL terminals.

I don't have pictures of my last similar project, as all of my belongings (including my computers) are in a complete upheaval, but I have seen some fuse-based services that are still in very good condition, they're not all fire hazards just because they're old.

I am basically in agreement with the others, however, MOST of them have seen better days and replacement is quite frequently the best option, but I just would replace it based on its condition, not "just because".


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RE: Using two fuses to create double-pole for 240v

"...I just would replace it based on its condition, not "just because".

"Its condition" is that it is not adequate for the new load being created.


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RE: Using two fuses to create double-pole for 240v

Thanks for all the replies. Wayne solved this problem, but my computer was messing up, so I couldn't close this thread sooner.

It is indeed the case that this is a 100-amp box, intended to have dual 60-amp main fuses, and dual 40-amp range fuses, thus adding up to the full 100 amps. The "main" pull block kills the power to everything except the "range" block, which feeds off the POCO's main lines at the same place the "main" block does. There is even a diagram on the box explaining this, but I failed to understand it until Wayne gave his explanation. Thanks, Wayne.

This leaves me with 40 amps for my electric range, and the remaining 60 for everything else: the water heater, the television, the computer, lights, etc. - which is more than enough, as this house doesn't use much electricity, since there is no A/C, electric heat, or other fancy stuff. Taking out 25 amps for the water heater, I've got 35 for everything else, and I couldn't use 35 amps if I turned on every light and appliance in the house. Between the TV, computer, refrigerator, lights, fans, kitchen appliances, well pump, etc., it adds up to 23.7 amps total, with everything I own running at the same time (a situation which has yet to occur).

I will not be replacing the fuse box. It is properly-sized for my needs, and for the POCO's 100-amp input, and it is in like-new condition. All of the house's wiring was replaced in recent history, as previously stated, so there is no burned/toasted/dry-rotted wiring anywhere on my property. Nothing is overfused, overloaded, or undersized. I personally prefer fuses over breakers, since any fuse will tell you what no common circuit breaker can: whether the blow/trip occurred because of (a) an overload, (b) a short-circuit, or (c) a power surge.

I sincerely appreciate all the replies; I got all my questions answered, and it didn't cost me a dime. Glad I used this board.


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RE: Using two fuses to create double-pole for 240v

That would be 35 amps at 240 volts. Or 70 amps at 120 volts. So are correct you should not have a problem.


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RE: Using two fuses to create double-pole for 240v

You should at least place a disconnect near the water heater that opens both of the hot lines.

A pair of cartridge fuses in an insert accomplish this and can serve as the required disconnect if they are withing sight of the water heater, but a pair of Edison base fuses do not crate the required disconnect.

It has to be a single device.


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RE: Using two fuses to create double-pole for 240v

time to upgrade to a 100 or 120 amp circuit breaker box.
The real problem with these old boxes is that they are rusting....and changing them is when you find out the grounding bar is disolving, and you just broke it (lol).
Your "range" pull out, could be used to wire an auxilary box, or you might find a post to connect a new auxilary box..But I doubt it...those old boxes have two or more wires going to every fuse.


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RE: Using two fuses to create double-pole for 240v

Is there some reason you came FOUR YEARS after the last post in this thread to give the wrong answer.


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