I am needing to drill some anchor bolts into concrete using an electric Hammer Drill (Electrical Rating 120VAC / 60Hz / 10A). I am working in a warehouse, and the worst case scenario, the furthest anchor point from a receptacle is 200 feet. In the past, I saw a company use a box that apparently bumped the voltage up (to regulate it) to account for the voltage drop. I have NO limitations here (other than distance) to consider when helping me.

What is that 'box' called. I searched the internet for regulators, but the only thing I could find was power inverters for vehicles. Can you please point me in the right direction. I am trying to avoid having to rent a generator like I did the last time...they're LOUD and exhaust fumes indoors is deadly.

  • 1
    200ft doesn´t sound that large a distance to run an extension lead for that hammer drill. Just use a decent section of cable, ie at least 2,5mm²
    – F. Bloggs
    Jul 15 '16 at 16:52
  • 2
    They are expensive but you can by 100 foot 10 awg extension cables - or rent a generator.
    – user51490
    Jul 15 '16 at 16:52
  • 3
    Can you rent a Honda EU2000 or EU3000? They are very, very quiet (one reason why they are 2x or 3x cost of other generators). Leave some doors or windows open or run a shorter extension cord and leave the generator outside.
    – Vince Patron
    Jul 15 '16 at 18:01
  • 3
    Renting a generator is cheaper than buying a boost transformer or a constant voltage transformer.
    – user51490
    Jul 15 '16 at 21:49
  • 3
    You may be a bit screwed here -- 10A@120V requires 8AWG to keep the voltage drop acceptable over 200'. Jul 17 '16 at 2:37

To directly answer your question: what you want is a "voltage regulating transformer". Alternately, I have also seen the wording "voltage regulator converter transformer" - basically add "transformer" to the search terms you're already looking for.

The issue is, in order to counter the voltage drop, you need to start at a higher voltage, so you need a transformer before the regulator. Likely you will need a 240/120 V step down transformer (most common). In theory there could be a 110V/120V+ step up transformer that will do a slight step up before the regulator so the regulator can regulate it down - but I can't find a specific commercial device that does that. Hopefully there's a 240V plug available to you, as well.

That being said, you should take the comments that have been made into consideration. It's likely much cheaper to just get a thicker extension cord (especially consider you'll probably at least need a new 220 V cord for the transformer anyway). The bigger the conductor cross-section, the less voltage drop per foot you'll experience. You can do the calculations to figure out what size you need, I suspect 10 AWG as was suggested will probably be sufficient for 200 ft.

  • I have access to the 240, so how expensive would it be to step it down, plus, that outlet/source is 300 feet away. I would think that you'd want the Step-Down Transformer pretty close to the outlet, correct? To answer others' questions....I have 4, 200 foot sections of racking to anchor to the floor. There will also be more to do in the future as I replace old racking and move it. In total, with these 4 sections, that equates to 84 anchors.
    – Mark
    Jul 20 '16 at 20:29

Your hammer drill doesn't seem very high power (with max 10A at 120V, it's max 1200W), so probably you will be better off purchasing an industrial battery-powered hammer drill of comparable power like this one (note the 36V battery pack rating, well higher than more hobbyist tools, which rate at less than 20V) or this one (disclaimer: just did a quick search on google, I haven't tried those models, so it's not a purchasing advice, but just an example of what exists).

What you'd spend could well be on par with the price of any sort of transformer or generator, and you'll have a very versatile tool that could ease other parts of your task.

Moreover, probably you could find someone that could lend you one or a store that could rent you one.

BTW, if you go the route of purchasing a cordless hammer drill, you could ask advice at Home Improvement SE.


If the voltage is not already a little low at the outlet, you can probably get by with a #14 AWG extension cord. The voltage will be about 10% low for 10 amps and 200 feet. A #12 AWG cord will drop about 6% and a #10 AWG cord will drop 4% under the same conditions. The box that you have seen used was probably a non-isolation boost transformer.


The box may have been a "variac."

Flowchart for your problem:

1) Do you have a 200 foot extension cord? If yes, try that first, I believe it will be no problem. But if it IS a problem, go to step 3, rent a generator and ventilation fan.

2) If you don't have an extension cord long enough, buy one then go back to step 1.

3) Rent a generator and ventilation fan. For the time it takes to do the job. Also rent a heavy-duty fan to blow clean air into your work area. Use the philosophy of blowing clean air to where you are, rather than trying to blow exhaust out.

Everything else is going to be more expensive.


Thinking about this, maybe you mean an AC voltage stabiliser? Something like this? They´re used a lot in the audio industry, less common for your situation.


I use a battery-powered hammer drill.

Might be cheaper to run a permanent outlet and use a 25' (or less) extension.

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