This is a spur of thread What's Dirty Power

Some questions about the implications of dirty power for the homeowner:

1. Would circuit breakers be tripped by voltage levels that were outside operating standards (whether high or low)?

2. If the answer to #1 is Yes, and they were (tripped), what is a good way to determine whether service is back to normal?

3. If current levels went outside operating standards (assuming that voltage remained normal), would the effect depend on how much current was being drawn at the time?

4. Would circuit breakers be tripped by harmonic distortion that was outside operating standards?

-- David L (bumpkin@dnet.net), December 06, 1999

Answers

1. No. Breakers work based on what is pulled through them rather than what is sent to them.

The real problem will be when a compressor (refrig or freezer) tries to start and there is not enough amps to start it. It it does not have protection for that it will burn up.

This is also true of any electric motor (well pumps for instance).

The issue is will there be enough power, not what if there is too much.

-- Not real sure! (cai2k@flash.net), December 06, 1999.

Under most circumstances it can be assumed that the resistance of the elctrical system is fixed. In a condition of fixed resistance, the relative values of current and voltage are inversely proportional. Therefore, as voltage rises, current drops and as voltage drops, current rises. By monitoring line voltage, one can maintain a relative view of what the 'power' is doing.

There are several manufacturers of a few different pieces of electronic equipment which you can use to monitor your line voltage.

The 'best' is known as a line level strip chart recorder. Basically it draws a line on a narrow strip of graph paper that is marked by amount of voltage varying from a standard ... in the case of home power, 120vac. Nice feature is a record of voltage changes ... great for determining if there is a correlation between time of day and line voltage. Bad part is ... need a good supply of the special paper for the unit. Available at industrial electrical supply stores.

Next option is a line voltage meter ... easiest here is to buy an inexpensive multimeter/multitester that has a 200 vac range, a cheap extension cord and two barrel plugs that will fit into the multimeter ( radio shack, etc ). Cut off the female side of the extension cord and attach the two connectors onto the wires. you end up with a wire with a male electrical plug on one end and two male barrel plugs on the other.

Plug the two barrel connectors into the voltmeter;

(NOTE: ac voltage is non-polarized so which plug in which meter input jack is irrelevent, just make sure they are in voltage and common)

(NOTE 2: WARNING - make sure you do not use the current input jack - you will fry either shunt resistor in the meter, or the meter itself)

Set the meter for 200 vac range and plug the other end of the wire into an electrical outlet.

Measure and record the voltage.

It is a GOOD idea to start monitoring NOW! That way you KNOW what normal is! (If there is such a thing!)

-- hiding in plain (sight@edge. of no-where), December 06, 1999.

I've been a Linemen for 26 years. I'll try to answer your questions,

#1..Amperage is what trips breakers. Remember, heat is what trips the breakers open. Voltage itself has vertually no heat. A 20 amp breaker will trip open if the amperage exceeds the 20 amps rated over a period of time. If you have motors connected to your home, refridgerater, fans, heating unit, low voltage will cause the motors to work harder. The amperage will rise and may trip your breakers.

#2. A volt meter to check your voltage from your wall recepticle is the best way. If you have a light bulb burning and it appears to be brown, you have low voltage problems. If your bulbs seem very bright or pop, you have high voltage.

#3. Dont understand your question., but I will try. If your voltage is at the industry standards, 120 volts, plus or minus 6 volts and your equipment is drawing more then the rated amperage for the size of your motor, your motor is working too hard or is under a locked rotor condition. The shaft that turns is seeing resistance beyond the norm.

#4. Yes, it is possible.

Just remember, it's the amperage or "current'' as it may be called, that trips the breakers, not the voltage.

-- Pl (Powerlineman@here.com), December 06, 1999.

Answer to 1. Unconditionally: NO!

Answer to 3. The current levels ARE what's being drawn at the time.

Answer to 4. NO. (Harmonic distortion is present in "modified sinewave" inverter outputs.) Odd loads may also distort line voltage. My engineering experience (in power) is that harmonic distortion of delivered voltage is NOT a concern for breaker tripping.

Your most important question was the first. It is BASIC that circuit breakers in homes are sized to National Electric Code to protect the WIRING (not the load!) They react to load current and nothing else. They are not even "thermal", they are magnetic (because that is cheaper). If one wanted to protect a load, one would have to add a thermal sensing device for those loads that could overheat. This is not done in home-use in the distribution panel, but appliances may have built-in thermal cut-outs. (Submersible pumps have them.)

Perspective: There is a basic level of immunity to power line disturbances built into most electronic gear. That specification may not always be available to the end user. It is "invisible" to the buyer, but it adds to cost nevertheless. Therefore, the degree of immunity varies widely, and you have no idea what the exact limits are for a specific item. In addition, proper design requires a safety margin above the minimum immunity. (This is where the engineers battle the managers.) Anyway, the situation is a bit better than you may assume, as dirty power is rather common during thunderstorms or ice shedding from power lines, but not for extended periods.

A significant exposure that may not be commonly covered is an extended time of severe undervoltage! If the design is proper, a device will shut down under such circumstances before it fails catastrophically.

-- W (me@home.now), December 06, 1999.

First, if you expose wires in order to connect a meter or other such device, be careful, and you might find it prudent to tape up with an insulating tape.

Meanwhile, low voltage conditions will lower the amperage drawn by resistive loads such as incandescent light bulbs, which may cause them to be noticeably dimmer than usual.

However, common AC motors behave very differently, and will often draw more amps when the voltage is low. They usually require extra amps until they get up to speed, but if the voltage is low, they may never get up to speed. So, they may then continually draw extra amps (and overheat).

So, if your lights go dim for more than a few seconds, or if they continually fluctuate, turn off any device that uses an AC motor, including fridge, oil burner, water pump, etc. In such a situation, it may be prudent to turn off everything except one or two incandescent lights until things get back to normal.

Jerry
P.S. for hiding: regarding the statements: "Under most circumstances it can be assumed that the resistance of the elctrical system is fixed. In a condition of fixed resistance, the relative values of current and voltage are inversely proportional. Therefore, as voltage rises, current drops and as voltage drops, current rises.", I must differ.

With inductive loads, such as common AC motors, the resistance is not the major controlling factor; it's the inductive reactance that counts, and in the case of such motors, that varies with the speed. The "locked rotor" current may often be 5 to 7 times "normal" operating current.

As for voltage and current being inversely proportional, that is so for a given wattage, but not for a given resistance.

-- Jerry B (skeptic76@erols.com), December 06, 1999.

While undervoltage (i.e., "brownout") conditions are indeed the most common type of "dirty power", they're far from the the *sole* type.

You can also experience overvoltage (both sustained and transient (of varying lengths), and of varying voltages). And, you can experience *unbalanced* voltage, although from what I can tell, that's *usually* localized to the local distribution transformer outlet, your inside distribution box, and everything inbetween. It's generally caused by a bad neutral connection. The symptoms are unique -- for example, your dryer turns on, and your lights, instead of dimming, brighten or burn out.

You can also have *frequency* problems -- either over or under 60 hz.

There has been a lot of non-wild conjecture that we've got a good chance of seeing a mix of non-trivial dirty power artifacts starting at midnight GMT on The Day. I don't plan on being connected at that time. I figure if the VA (or was it SSA?) thinks it prudent to switch to their generators for the Magic Moment, I'll take my cue from them.

-- Ron Schwarz (rs@clubvb.com.delete.this), December 06, 1999.

Jerry - you are, of course, absolutely correct ...

All I can do is to apologize to all for my mis-statements and offer up a feeble excuse of "I went brain dead there for a few ... brain processing about power and fingers went off into an auto mode doing there own thing..."

... Guess it's time to chunk my MSEE into the kindling pile ... been outta the industry too long ... sigh!

-- hiding in plain (sight@edge. of no-where), December 06, 1999.

Hiding,

And I thought you were just testing to see if we were paying attention. :-)

Jerry

-- Jerry B (skeptic76@erols.com), December 06, 1999.

At local noon or prior to 2400 GMT, turn off and UNPLUG all electronics and non esential equipment.

I am going to empty one of my refrigerators and unplug it. I will leave only one TV plugged in and turned on.

Remember by lunch time USA we should know what happened in the Orient, India/Pakistan, and possibly the Holy Land and Russia

-- woody (woody11420@aol.com), December 06, 1999.

Supplement:

Not wanting to push anything... Radio Shack has plug-into-outlet expanded scale voltmeters. Very useful to see what's going on. Also reasonably correct for modified sinewave inverters!

....Frequency variations ARE A MYTH!!!

as long as the power is from the grid! The fact that many specifications show a +/-.5 or +/-1Hz variation only means that the equipment tolerates it, NOT that it is present. Indeed, the grid could not exist with such variations. (Visible: electric clocks that operate on 60 Hz power. Technical proof: skipped, this is not an engineering forum.)

Another perspective: a home generator(!) could provide dirty power, INCLUDING frequency variations. (You know it when your refrigerator starts.) Do NOT use your generator in standby/idle position (if it has such a switch), if you start motors of any kind from it.

-- W (me@home.now), December 06, 1999.

W,

Thanks for the tip on the plug-into-outlet voltmeter. That could be very handy for folks who want something better than guesstimating the intensity of their lightbulbs, but don't have other stuff on hand that will enable them to see what the juice is doing.

Jerry

-- Jerry B (skeptic76@erols.com), December 07, 1999.

Great information! Thanks, everyone.

-- David L (bumpkin@dnet.net), December 07, 1999.

Frequency variations have happened before during various catastrophes.

Regardless, if there's widespread islanding, it obviates any protective measures delivered *by* the grid.

IOW, if you're expecting your generator to remain on-frequency because it'll be phase-locked to the rest of the grid, you'd better have a "Plan B" in the event that from your generator's perspective there *is* no "rest of the grid".

Personally, while I *will* be off-grid during The Grand Moment, I will *likewise* be watching a volt meter and frequency counter that *are* set up to monitor the grid.

(I recently discovered that my Radio Shack frequency counter will not only measure the frequency of our GMRS radios, but will *also* measure right down to DC. Set to the lowest range, with the antenna extended, it picks up the stray potential in the house and displays "60".)

-- Ron Schwarz (rs@clubvb.com.delete.this), December 07, 1999.