Electricity 101 - Reading Recommendations?

[PharmGeek]

Perry, why do you think that 50amp service cannot supply two running AC units? if a single 30amp 120v can run one, it stands to reason that two 50amp 120v legs can run those two...and perhaps a bit more as well...?

I suppose load testing with various appliances will help.

Oh and I will use the quality surge protector mentioned ("TRC surge guard") which shuts things down if voltage is too high or too low..

[PharmGeek]

and that is a good point perry...I did see in various links in this thread descriptions and youtube video about how to use a multimeter and test 30 and 50amp voltage as you described....gives me a bit more confidence

[lewster]

Originally Posted by perryg114

Learn to use a digital volt meter (DVM) and also learn what each pin does. On the 50A socket there are two hots a neutral and a ground. There should be 0 V between the ground and neutral. There should be 220V between the two hots and there should be 120V between either hot and the ground and neutral. A volt or two is nothing to worry about. If you are running a 50A trailer make sure you know how the power is being distributed. Things like not running the microwave and the AC at the same time. Not running 2 AC units at all.

The DVM is the Swiss army knife of electrical tools. You can also get one that measures current so you can measure how many amps you are using. You can use it for AC or DC and also resistance so you can check for shorts and open circuits etc. A DVM should be a part of your tool kit.

Perry

Quite the contrary!

When an RV uses a 50 amp service, it load balances the large drawing appliances over the 2 separate 50 amp 120VAC feeds. There is absolutely no danger running 2 roof A/C units together at the same time. Large motor homes do it all the time. Airstreams with 50 amp service, connected to a 50 amp power pole will provide sufficient AC amperage (wattage) to power both roof A/C units at the same time. You can even run the microwave at the same time, provided that your total amperage is below the individual 50 amp leg's capacity.

If you have only 220 VAC between the 2 hot legs, you are almost 10% below the standard voltage, which is 240VAC, or 120VAC per leg. 108VAC, or 216 VAC for the 2 legs is reaching the lower threshold for proper operation of AC appliances.

[PharmGeek]

ive heard 100 and now 108....if <108, this is a problem then? What happens in such a case? Or what can happen (i presume higher loads more likely to flare up the issue?).

The TRC safeguard will protect from lower voltages as well correct? At what point does the TRC unit trip? 108? 100?

[perryg114]

The 50A service is 50A x 220V or 11,000W a 30A service is 30A x 120V or 3600W. The 50A service is 3 times more power than the 30A connection. You can run both AC units the microwave and an electric hot water heater. P=IV and V=IR ohm's law.

Remember your physics courses.

Perry

[lewster]

Originally Posted by PharmGeek

ive heard 100 and now 108....if <108, this is a problem then? What happens in such a case? Or what can happen (i presume higher loads more likely to flare up the issue?).

The TRC safeguard will protect from lower voltages as well correct? At what point does the TRC unit trip? 108? 100?

Not sure of the exact spec on the TRC, but they generally run +/- 10 %, which gives you a range of 108-132VAC. At lower voltages (brown out), the amp draw of a given appliance rises and can easily trip a circuit breaker or damage the appliance. The TRC would shut the incoming power in a low voltage situation like that, saving a potential melt down in the trailer.

[PharmGeek]

@Perry...I took two semesters of physics in pharmacy school...I have repressed it...trying to think about it induces PTSD!

@lewster - got it....good to know...follow up question then....lets say you get to a camping spot - the readin is 107 or 108 (or some number lower lets say)....at what point do you just forgoe hooking up to that hookup alltogether?

[lewster]

Personally, I never hooked up at a pedestal lower than 115VAC. I would ask to look at a few other sites and if they were all that low.....change campgrounds!

[PharmGeek]

sorry, dont mean to be really detailed, but it seems from my reading and discussion so far that common RV folks benefit from checking for proper voltage..if too high, then do not plug in...too low, then do not plug in...if polarity is screwed up...same. Surge protector a good idea to protect from such things as they

But I guess it may be instructive to perhaps list out or lay out a number of scenarios where we should not plug in...and be specific.

for example at x low voltage, or at y high voltage, or if the cord looks melted from possible previouis over-heating.

It is certainly good to know that that even if I miss something, the surge protector will trip with most of these issues.

Thanks you all...this has been very helpful!

[PharmGeek]

woops, lewster, did not see your last post before posting last...noted....thanks.

[mimiandrews]

One more book you might consider:
RV Electrical Systems by Bill and Jan Moeller.

[perryg114]

If your are getting less than 110V with no load then you have a problem. Anything less than 100V under load is going to start burning things up. The power disipated in a device is the current squared times the resistance. So things really start to heat up as the current rises and the voltage drops. This is the same reason you need big wires to run small loads at 12V. To run 1000W at 12V requires 83A. To run 1000W at 120V it takes 8A. This is also why running your fridge on 12V will suck a battery down in no time at all. 300W/12V = 25A.

Perry

[SteveSueMac]

Originally Posted by lsbrodsky

The plug on the right and the yellow polarity tester are all you need to check any 30 amp safe for your trailer. Just plug it in look for the correct lights, unplug it and plug in you shore power cable. I have done something similar at marinas for 30 years.
It is not going to tell you whether you draw too many amps for an inadequate shorepower service, but with a normal campground 30 amp and a stock trailer that should not be an issue.
Larry

In another thread on surge protectors, I followed a link to this: http://www.progressiveindustries.net/ems_pt30c.htm

It seems this unit tests for all the issues you'd want to test at the post (accidental 240v installation, reverse polarity, open neutral, open ground) and in those cases will not send power to your RV. In addition, if the voltage is too low/high, it will shut down to reset and if a surge will protect your electronics. While fairly expensive, it seems like an all in one option for testing and surge protection. Am I seeing that right and if so, how the heck does the lock part work? :-)

[mimiandrews]

Originally Posted by SteveSueMac

In another thread on surge protectors, I followed a link to this: EMS-PT30C

It seems this unit tests for all the issues you'd want to test at the post (accidental 240v installation, reverse polarity, open neutral, open ground) and in those cases will not send power to your RV. In addition, if the voltage is too low/high, it will shut down to reset and if a surge will protect your electronics. While fairly expensive, it seems like an all in one option for testing and surge protection. Am I seeing that right and if so, how the heck does the lock part work? :-)

We have one of these and like it very much. The "lock part" is only a ring that can be used with a cable-type lock to secure the device from theft. It's aluminum and would be easy prey for a pair of bolt cutters.

Instead of that, I use an extension cord so that the surge protector can remain inside the locked rear compartment of our trailer.

[daveswenson]

I continue to plug this one. (pun intended)

EMS-HW30C

Good protection, useful info from the panel, can't be stolen.

[SteveSueMac]

Originally Posted by daveswenson

I continue to plug this one. (pun intended)

EMS-HW30C

Good protection, useful info from the panel, can't be stolen.

Nice pun! :-)

I think the electronics are the same as the portable one, yes? Definitely advantages to the hard mount but not wanting to muck with the wires, I'm thinking portable. Do I understand correctly that it's pretty much an all in one tester, surge and EMS protector? If so, I'm ready to buy. Small insurance against big losses.

[daveswenson]

Originally Posted by SteveSueMac

Nice pun! :-)

I think the electronics are the same as the portable one, yes? Definitely advantages to the hard mount but not wanting to muck with the wires, I'm thinking portable. Do I understand correctly that it's pretty much an all in one tester, surge and EMS protector? If so, I'm ready to buy. Small insurance against big losses.

Same protections, hard wired or portable. Great unit. Hard wired unit was very easy to install.

1. Disconnect power.
2. Open transfer relay and disconnect 3 wires.
3.Connect those wires to EMS
4. Connect new wire from EMS back to transfer relay
5. Mount remote ( I put mine in the cabinet under the sink)
6. Reconnect power secure in the knowledge that your electrical stuff is protected and no one can steal the EMS.



Not rocket science.

[PharmGeek]

Cool - ill be considering these for sure

Still foggy on portable vs fixed?

[swampthang7]

I think I'll stay at a motel 8 tonight....no blown fuses and lots of hookers!

[daveswenson]

Originally Posted by PharmGeek

Cool - ill be considering these for sure

Still foggy on portable vs fixed?

I like the fixed, one less thing to store/lose.