Question for an Electrician...

[Traveler 45C]

Sort of!

In your first post, you said you were designing a circuit, what size breaker do I need. Later, you stated that the circuit you were using had a 20 amp breaker, which was tripping and was not G.F.I. protected. I think that is where the confusion came in.

Agreed.

 

[MikeP]

I'm sorry to belabor this but IF I understand you, you are thinking that IF there is a short the load will exceed 40A and therefore pop the breaker. But that's not true IF the wiring cannot handle the 40A in the first place.

The too-small wire will take the place of the circuit breaker and burn/separate/start a fire at some amperage level below that of the breaker. As an example, lets say you have a circuit designed for 15 amps. You install a 30A breaker in the box. Then there is a short circuit. The breaker, since it can handle twice the current as the wires would essentially see the short load the same as it would if you had turned on a 15 amp electric heater. The load on the breaker would never get high enough to trip it; the wire would burn first.

The breaker MUST be able to protect the wiring in case there is a short circuit which could be caused by a variety of unforseen reasons. So if you really need a 40A breaker for this motor, you must run new wiring of sufficient gauge to handle 40A continuous load. Otherwise you risk a fire and additionally the circuit would not be acceptable to any inspector - either land or marine-based.

I apologize for rattling on about this but there can be serious danger involved with mismatching wiring with breakers/fuses. So be careful!!!!

 

[Traveler 45C]

Lets again use your 15a household ckt. Lets say we replace the 15a with the 30a and then run a vacuum cleaner pulling 12a. The wiring is able to handle that load and all is well. Now lets run 2 vacuums with both pulling 24a. In this case your right, the wiring is too small for the load and will get hot, possible starting a fire, meanwhile the breaker never pops.

Now lets take the same ckt, one vacuum and either run over the vacuum's power cord with some type of sharp metal creating a short or create a short in the motor. In this case, and this is the point I'm trying to make, total house current available (100-200a) will flow through the wiring and breaker, but for only an instant because the breaker will certainly pop, the wires won't have time to heat up. This works because the current will only be there for an instant, not continuously as in the example above.

That's what I got from the research and I understand the theory. However, although this was planned to be a dedicated ckt for this motor, if I size up the wiring like ya'll are screaming at me to do, I could use it as an extra outlet. So that's what I'll do.

 

[Traveler 45C]

Wow, all that and you are back to sizing the wire to correct gauge.

I don't believe I ever said what gauge I was gonna' use...

I was just tryin' to find out what size breaker to use...

Geez!

 

[krush]

True statement but a short in the ckt, should that happen, will pull a whole lot more than 40a. True also that the wiring must be able to carry 40a if you have a 40a breaker and will be using that much current to drive a load.

Maybe....and "in theory". You can have a short that isn't going to pull enough current to trip the breaker, especially if the wiring is undersized. But honestly, I'm not going to arguing on an internet forum with somebody that doesn't know what he is talking about. You thread title is "question for an electrician". Don't ask the question if you are just going to argue.

But to help you solve your problem, breakers are designed to trip at their rated CONTINIOUS amperage. They are also designed to allow a higher inrush current for things like motor starting...but you don't have to take my word for it.

Breakers are designed to be able to safely carry a current in excess of their rating for very very short periods of time to allow some types of electrical equipment (called inductive loads) such as motors to start up.

http://www.mikeholt.com/mojonewsarchive/EES-HTML/HTML/ElectricalCircuitBreakers~20030621.htm

The NEC has all the answers...this isn't rocket science.

 

[TedZ]

I am particularly happy to see that the NEC "has all of the answers." It is, and has been my position that while there are many electrical items and methods unique to boats, that in fact the NEC does the overwhelming amount of testing and that there are probably 100,000 (guess) houses, buildings and plants to every boat. Accordingly, they have a lot of experience in what can and does go wrong. Items more stringent than the NEC particular to boats should be followed. Items less stringent than the NEC, for example grounding, should be more carefully evaluated and tested before following blindly. Conventional practices in the boating world are "conventional" to only a very small universe.

The NEC is easy to follow as a minimum. It is correctly stated here, "it is not rocket science." If you deviate from it, you really need to have a better reason than xyz manufacturer does it that way.

Ted

PS Not soft starting this motor is just plain stupid, sorry to plain talk. All of the screwing around you folks are talking about for want of a $10 item! Inrush goes to maybe 1/4 - 1/3 times normal, the breaker doesn't trip and no wiring needs to be changed. Plus shopping and wiring something you don't use all of the time is educational and may provide a lot of $$$ savings in your businesses, i.e. having the demand meters run a lot less!

 

[Mako440]

Trav,
"I" wasn't "screaming" at you to size up the wire. I was just pointing out what the "minimum" should be.

And, the NEC is "rocket science" as there are many exceptions which tend to confuse people who do not deal with the code on a daily basis.
For your situation, we haven't got into load calculations as it pertains to your entire boat, or any of a number of things that could be affected by what you are doing. That is why I recommended an electrician be called. For $200.00 you could probably have had this done already!

Back to exceptions in the NEC. Here is one, if your home was built in the 50s and you have a two wire (no ground wire) cloth insulated wires with two prong receptacles, and you want to change them to three prong receptacles, how do you do it?
Do you change the receptacles and say it is OK? Rewire the home, or, is there another option?
There is another option. Add G.F.I. receptacles and mark them ungrounded, although, I would trecommend method 2.

There are also very different interpretations of the code. For me, I like to exceed the "minimum". Then I don't have to worry if it "meets code".

 

[krush]

For crying out loud: motor, wire, fault/overload protection. That is all this thread is about. Simple stuff. Black and white. Easily covered by common sense and backed up by NEC. Nothing special for boats.

HOF strikes again in turning a simple problem into a 2 page argument LOL.

 

[TedZ]

Soft start units are used after the original breaker. There is no way they provide less protection.

Do you want examples and URL's? Impugning soft starts takes away one of the best green/money savings devices out there. That and power factor correction are the tools we have to use less power, lighter feeds and safer installations. Figure it out. If you blow the breaker without soft start and you don't after a soft start installation then the conclusion is obvious. Try it.

BTW they are not either zero voltage or zero currrent devices. They start with both reduced, and ramp up both with time, generally a few seconds.

Ted

 

[SKYCHENEY]

Speaking of power factor, I was interested to see that on a 1978 60C, Hatteras had installed a box full of capacitors that were hooked to all of the A/C units. I assumed this was for power factor correction. What do you think, Ted?

 

[TedZ]

Craig,

You are one of the best electrical guys on the forum...your answers are always valuable.

Everything you say is correct but soft starting small motors is practical because of more robust solid state soft start devices. The ones i have used are active devices, i.e. have some intelligence as opposed to just being a triac or other passive device. As you say they are a must for us up in the Northeast on motors of 100HP and more.

http://www.squared.com/us/products/motor_control.nsf/unid/2800F8DEA2CC3B3A85256A1F005F6A57/$file/SoftStartOverview.htm

There are lots of examples. I like Square D stuff so i included this one. Search "soft starters," There are hundreds.

Power Factor correction is absolutely facinating because the savings for light to heavy industry is unbelievable. Even a small business that uses a lot of AC can cut the power bill a lot. Without going crazy here, the lag or lead of the voltage vs. amperage curves are corrected using capacitors. An unbalance between inductive (motors) and reactive (lights, heaters) power can spin your meter but you don't get the power. Strange, i know. The unit is KVAR. Remember KW = KVA * PF where PF is the power factor. "Things" are designed usually with a .8 PF. If the PF is worse than that (rare) they won't perform. Better than that they perform better, i.e. use less ampacity than on the nameplate. KVAR is KVA Reactive and is the Cos Theta where theta is the angle of an elipse formed when a laissez jous pattern is shown on a dual trace scope measuring voltage and amperage. Too much info i know, but if it wets your appetite for further discovery, you will enjoy it.

This is a much misunderstood field. Anybody Google "power factor correction" and if it is not clear, start a topic on it to get everyone's questions and input. The smart thing is for the marina to correct for the whole connected load. Individually for a boat, it is not wonderful unless you run a lot of motors.

Lastly, the caps on your boat are likely the caps for compressor motors remoted because many of the AC motors are sealed in pressure domes and the caps would not like that. It is very unlikely they are for PF correction.

Ted

 

[krush]

Power Factor correction is absolutely facinating because the savings for light to heavy industry is unbelievable. Even a small business that uses a lot of AC can cut the power bill a lot.

Because I'm too stupid to not argue, please show me where a small business or home owner is charge for reactive power. It's usually only in industrial applications that a reactive power meter is installed and the user is penalized for lower power factor loads (because it pisses off the generator, literally LOL insert Bill and his MVAR comment)

In a residential or small biz application, the meter only tabulates real power (and charges for real energy). Thus, us little guys aren't penalized for low power factor loads because it isn't worth the trouble for the power companies.

And what this means is that there is no $$ savings due to "lower energy costs" if one installs any type of power factor correcting equipment in their house or boat--the power company doesn't even record it.

 

[TedZ]

Well this is why i say this is not well understood. There is no power factor meter of any type supplied by utilities.

Maybe this helps:

Quote "The significance of power factor lies in the fact that utility companies supply customers with volt-amperes, but bill them for watts. Power factors below 1.0 require a utility to generate more than the minimum volt-amperes necessary to supply the real power (watts). This increases generation and transmission costs. For example, if the load power factor were as low as 0.7, the apparent power would be 1.4 times the real power used by the load. Line current in the circuit would also be 1.4 times the current required at 1.0 power factor, so the losses in the circuit would be doubled (since they are proportional to the square of the current). Alternatively all components of the system such as generators, conductors, transformers, and switchgear would be increased in size (and cost) to carry the extra current.

Utilities typically charge additional costs to customers who have a power factor below some limit, which is typically 0.9 to 0.95. Engineers are often interested in the power factor of a load as one of the factors that affect the efficiency of power transmission." End quote.

Trust me you are paying for bad power factors everywhere but it is not significant in boats, residences and some small businesses. Sometimes it is. I thought i made it clear that doing PF correction on a boat was not particularly valuable. Obviously, small loads don't get charged a PF penalty by the utility company.

The quote above was taken from http://en.wikipedia.org/wiki/Power_factor
which does a nice job.

Make no mistake. Bad power factors cost you money even if you live in a one room house near the railroad tracks! It is not a concept that is easily understood as a portion of the power simply disappears i.e. is returned to the utility company without doing any useful work for you. The meter records it all and doesn't give you a credit for the power not used (reactive power) that is returned. Saying things like "the power company doesn't record it" and "the meter ony charges for real power" are simply wrong. Sorry but i don't know what else to say except research it more and carefully learn what this is all about. It is fascinating and could save some of you a lot of money in your various businesses.

Ted

 

[MikeP]

Like Krush said earlier, who would have thought that we could start out with a "what size breaker do I need" question and end up with something like, "Line current in the circuit would also be 1.4 times the current required at 1.0 power factor, so the losses in the circuit would be doubled (since they are proportional to the square of the current)"

I don't even know what the heck that means!

 

[krush]

Well this is why i say this is not well understood. There is no power factor meter of any type supplied by utilities.
................................

In certain cases (large commercial and industrial users that tend to have high inductive loads) a reactive power meter (kilovar-hours meter) is installed and compared to the kWh meter and if they are vastly different a surcharge is applied, like at this utility: http://www.bchydro.com/powersmart/t...es/power_quality/power_factor_correction.html

Utilities typically charge additional costs to customers who have a power factor below some limit, which is typically 0.9 to 0.95. Engineers are often interested in the power factor of a load as one of the factors that affect the efficiency of power transmission." End quote.

Trust me you are paying for bad power factors everywhere but it is not significant in boats, residences and some small businesses. Sometimes it is. I thought i made it clear that doing PF correction on a boat was not particularly valuable. Obviously, small loads don't get charged a PF penalty by the utility company.

See above response. Unless you have two meters or a meter that measures both kW-h and kVar-h, you will not be DIRECTLY charge for having a low power factor. The utility may increase their rates to all uses to account for low power factors in the system, but you will not DIRECTLY pay a surcharge as in the link provided above.

Make no mistake. Bad power factors cost you money even if you live in a one room house near the railroad tracks! It is not a concept that is easily understood as a portion of the power simply disappears i.e. is returned to the utility company without doing any useful work for you. The meter records it all and doesn't give you a credit for the power not used (reactive power) that is returned. Saying things like "the power company doesn't record it" and "the meter ony charges for real power" are simply wrong. Sorry but i don't know what else to say except research it more and carefully learn what this is all about. It is fascinating and could save some of you a lot of money in your various businesses.

Ted

Make no mistake....please tell me how much experience you have with this topic other than what you read on the internet/wikipedia.

Make no mistake again: I don't need to research it more because most of my professional career has been in power generation and distribution. I've been in the operator room of plants when operators have had to address "controlling their Vars".

Finally, don't make this mistake. Don't assume that your internet research is always going to make you more educated than somebody else on "a concept that is [not] easily understood."



Now for those that are reading this and have no clue or don't understand the topic, here is a nice analogy in picture form provided by the link above:

Train Analogy Diagram

Imagine a locomotive pulling a boxcar on a parallel train track with a chain. The tension in the chain is higher due to the sideways component of pull but the work done in moving the boxcar is exactly the same as if the locomotive was directly in front of the boxcar requiring a much lower chain tension.

The increased tension in the chain when pulling from the side is analogous to the increased current necessary to supply the reactive power in an electrical circuit. The chain has a limited capacity for tension before it will break just as electrical wires have a limited capacity to carry current before failing. By increasing power factor (putting the locomotive in front of the boxcar) capacity is freed up in the electrical system (the chain has more spare tension before reaching the breaking point).

 

[TedZ]

One of the things i do is install generators and power factor correction equipment. My last job, a few months ago, was consulting on a PF installation at a micro brewery with a lot of cooling equipment.

My post came before i read the Wiki post and i was surprised to see we were both on the same track. They didn't mention laissez jous diagrams. Google that and you will find nothing. Ask any EE and they will tell you what they are. They did mention different measuring techniques which was illustrative i thought.

I work in NY, VT, CT, and MA and i have never seen a KVAR meter. Your site says they exist, fine, but our utility companies are not that helpful in reducing industrial power bills. Maybe they bill by that meter, i don't know. Our tariff alows usage and demand meters only.

What is it Krush you want to be the electrical go-to guy on HOF? OK with me. I try to give my thoughts without putting anyone else down. I get paid for my advice that i give for nothing here. I guess that is what it is worth.

You work in the industry. You answer the questions.

Ted

PS You are lost in the direct charge notion. Power factors away from unity cost you money because your regular, plain old household meter spins more with bad pf's. You don't need a special meter to get billed more! Depending on the size of your mansion, there might be a fair amount of money to be saved.

 

[krush]

PS You are lost in the direct charge notion. Power factors away from unity cost you money because your regular, plain old household meter spins more with bad pf's. You don't need a special meter to get billed more! Depending on the size of your mansion, there might be a fair amount of money to be saved.

I only trying to correct misinformation. The meter on almost all houses only measures real power; you say it measures apparent power (which includes reactive power). This means power factor not of a concern as a residential user because we are not directly charged for it. If I install $2000 of power factor correction equipement, my bill is not going to be any cheaper because I have a better PF. If the bill is cheaper, it will be a coincidence.

I will provide a few more sources to prove I am correct, but I'm done. Whether or not you chose to propagate misinformation is up to you.

Electricity utilities bill residential customers for only real power consumed, as opposed to apparent power. Industrial customers are more scrutinized as they are penalized for electric loads that have low power factors which create a large difference between the supplied apparent power and the power consumed by the load (real power)........Electricity retailers may use electricity meters which measure reactive power to financially penalize customers with low power factor loads (especially larger customers).

http://engineering.wikia.com/wiki/Electric_power

However, I’m not buying it. There are two great resources on-line that address this same issue. One is Energy Star and the other is a blogger I’ve been reading for 4 years and has a great section on electricity, Michael Bluejay. Both of these resources say power factor correction really wont help on your residential bill. It can make a difference for certain industrial users who may be billed by the Utility for peak demand, but this is another story (and it is addressed in the Bluejay article).

To go a little deeper, the formula for Power Factor (PF) is below:

PF = Real Power (Watts) ÷ Apparent Power (VA)

The power factor correction devices are said to improve the second half of the above equation, the Apparent Power. However you don’t pay your utility for Apparent Power. You pay them for Real Power (Watts). I would like to see more info from the manufacturers of these devices on how improving PF helps save you Watts! Basically, your utility doesn’t really care what your Power Factor is, so I want to see some evidence on how this device impacts your energy bill.p

http://blog.mapawatt.com/2009/03/31/power-factor/

In the second link he has links to other info from electrical engineers that also say there is no point in power factor correction for residential homes. In short, you've been scammed by marketing just like many consumers!


Want more proof and math, this guy even provides a rigorous analysis....Power Factor Correction Scam Review: http://www.nlcpr.com/Deceptions1.php

Residential customers are not penalized for having a low power factor. You will not save a single cent by using these devices in the home.It will not help your washing machine run better. The power factor is not on your utility bill. While power factor correction is valid for many industrial customers who use large amounts of power, it is a deception when marketed to home owners as a way to save money on their electric bill.