RV Power Panel Installation

[cbr046]

Could use some guidance . . . . We're looking to install an RV park style power panel 50A/30A/20A with breakers.  There's Eaton, Siemens, "American Made" and Chinese for ridiculously cheap (based on reading you get what you pay for - headaches!).

$178.50 - American made, 1-3 week backorder.  add $28.34 shipping + tax
http://www.rvparksupplies.com/p/503020AMPSMPOWER/

$72.50 - ships within 72 hrs from China
https://www.kueins.com/product/rv-panel-with-50-amp-and-30-amp-rv-receptacles-and-a-20-amp-gfci-receptacle/

$186.90 with mail-in rebate until 8/21 then $210 - Eaton box, Menards is a supplier in the upper mid-West.  add $14.55 shipping & handling + tax
https://www.menards.com/main/outdoors/outdoor-recreation-sports/camping-rv-supplies/rv-panels/eaton-50-amp-30-amp-20-amp-120-240-vac-outdoor-rv-panel/chu1n9n4ns/p-1444429546118-c-6440.htm?tid=-1482409728399190843&ipos=1

$245.73 - Siemens through Amazon.  includes shipping, add tax
https://www.amazon.com/TL137US-Temporary-Receptacle-Installed-Unmetered/dp/B00A8FQUYW/ref=dp_prsubs_1?pd_rd_i=B00A8FQUYW&psc=1

All are list prices excluding tax & shipping (Amazon is free shipping).  I'm leaning toward "RV Park Supplies". 

We'll also be installing a power cable from a metered power panel to the site, about 100 ft including vertical distances but doesn't consider bypassing a tree root system.  The panel has a 100A 2P unused breaker.  Question is, what do I need to specify for underground cable?  How deep to bury it (cable tv is inches, power is 3 ft?)?

We're in a rural area . . . . Anything else to consider? 

- bob

 

[Dr4Film]

Bob,

I think you have chosen the best one in my opinion for the money and quality.

[Cubflyer]

I believe the "standard" for buried power cables are 'min 3 ft' deep.  As for size of the wire, that is based on load and distance (and maybe type of wire...copper/aluminum).  You can probably find a chart for that online.... 50Amps---100+ feet.... = wire gauge.. "0" or "00" or ??  But since you are starting with a 100Amp CB the cable needs to be able to carry 100 amps... (the CB protects the cable, not the load).

I think you also should bury a 'tracer' streamer a few foot above the cable... but I do not know the rules on that...

Ken

Edited August 17, 2022 by Cubflyer
addition

[Tom Cherry]

57 minutes ago, Cubflyer said:

I believe the "standard" for buried power cables are 'min 3 ft' deep.  As for size of the wire, that is based on load and distance (and maybe type of wire...copper/aluminum).  You can probably find a chart for that online.... 50Amps---100+ feet.... = wire gauge.. "0" or "00" or ??

I think you also should bury a 'tracer' streamer a few foot above the cable... but I do not know the rules on that...

Ken

I would trust the Eaton one.  As far as wire goes, you need type UF (underground) or run conduit….plastic is OK.  The 3 ft is probably OK…but running it around a tree is a disaster.  I would use EMT there…the thicker kind that is hot dip galvanized.  You can mix and match…but remember that tree roots keep growing .  I would give the tree a wide berth….maybe go down 4 ft there.

Wire size needs to be #4 copper.  You can use THNN or single stranded insulated in the conduit,  probably need 1” or so.  The issue with the THNN compared to UF or a Romex Jacketed cable is the “pulling”.  If you used a 45 deg fitting and “bent” the conduit for getting around the tree, then maybe 1 1/2 “ conduit for the section of the tree.  So UF and plastic or EMT conduit for the arc around the tree.  Bend it with the UF in place.  BUT…pull it all the way…..with the straight run at the tree.  Bend an arch and bury it….

You do NOT want to do an underground splice.  YES….the power companies do it….but they do it all the time and they know how to coat and waterproof it.  I have done #6 splices and they are still good, but inside a garage and in a Junction Box….never underground….and I “know” how you are supposed to do it….but don’t plan on ever doing it.

Ordinarily, you could run #6….like what is in your rig.  BUT the voltage drop for the length kicks in.  I ran the calculator and you should be good, with #4 up to 75 amps or so…..then it clicked over to #3.  So, to have a 3% drop or less than 4 VAC on a 115 VAC  service or 111 VAC….you are OK.  If your feeder will deliver 121 or so, then you are fine….as it will be 117 at the pedestal.

That is my take….OK…obviously we have a discrepancy.  I found the Southwire calculator and ran it again.  It says, unless I misread it….that #4 will work.  This is a 120 VAC circuit…as the load will be split….therefore using 240 is not the way I interpret it.  The post with the 4/0 seems a bit overkill….  It matters not that the conductors are in conduit (THNN) or inside a Romex jacket.  Finding the right cable….then comparing THNN, using probably a # 10 Ground stranded to bare solid might be the trick.  I don’t buy wire that size like I did when I was in charge of maintenance.

I AM a firm believer in GROUNDS.  I would run a 8 ft driven ground at the pedestal.  The breaker on the Pedestal protects the wiring upstream to the breaker used on the main panel for this.  Therefore 50 A is correct there.  The #4 is rated for 85 amps.  I would put in a 75A or an 85A breaker at the main panel and not use the 100 amp.  Theoretically, the downstream 50 will open and protect the run,  75 -85 upstream will still protect the underground wire in case the 50A fails.  

AGAIN…that is MY interpretation of the code and past experience.  Talk to the electrician or the local county building inspector.  

[cbr046]

Gauge is easy . . . .

 

It's all the letters that dictate the right type.  Gives me something to research.  Thanks, Tom. 

If the breaker has the ability to supply 100A then I'll need to spec a cable to match.  Excellent chance we'll never see the full current unless we have 2 RV's connected, but you never know.  I'm leaning more toward #0. 

- bob

 

[Tom Wallis]

Correct me if I'm wrong but I think a 50 amp RV plug can provide 100 amps. Each of the two 120 volt circuits can provide 50 amps.

[Specialk]

If using direct burial cable, 2-2-2-4 aluminum, it will provide service at the 100 ft.  The minimum earth cover per code is 24” unless buried under concrete, then can be 18”.  The wire if buried, (not in conduit) is rated for 125 amp.  Therefore the wire is compliant with 100 amp circuit that you mentioned already exists.  However with a 100 ft run the voltage drop would be to great if you are in fact using all 100 amps of circuit?  Assuming you are using for the RV and likely not greater than 50 amp per circuit, (using only one of the 30/50 amp connections, not both simultaneously) then this wire and burying depth is code and will perform fine.  The maximum amps continuous ( with considerations to voltage drop) for this feed is slightly above 60 amps per line (2 lines), therefore you could still use approximately 1/2 of the 20 amp circuit for ancillary devices while on a 100% 50 amp load at RV, which is highly unlikely for an extended period of time.

The information above is based on the assumptions you noted as well the ones I’ve noted.   If you have additional information for how you to plan to use this, feel free to share.

 

Kevin
 

 

[Fasthobie16]

Buried EMT? How long would that last? 

[Tom Cherry]

10 minutes ago, Tom Wallis said:

Correct me if I'm wrong but I think a 50 amp RV plug can provide 100 amps. Each of the two 120 volt circuits can provide 50 amps.

Yes.  We seem to have a discrepancy in the choices of wiring chart or calculators.  The voltage to be used, assuming that a 50 amp 240 vac device (welder) is not used, is 120 VAC…..

I reran the Southwire….and used 240 VAC.  HMMMM.  The cable size dropped (got smaller) and Southwire says #6.  I ain’t gonna do that.  My gut feel, which Southwire confirmed, said to go down or larger to  the next size….which was #4.  #4 is also what a member used for his 50A service which was around 100 or so feet.  So, I think that #4 is fine….

 I 

[Tom Cherry]

12 minutes ago, Fasthobie16 said:

Buried EMT? How long would that last? 

Well, that probably depends on the pH of the soil.

But, you did raise an interesting point.  Don’t know if there are other sources, but this one popped up first.  I DO remember a run where we encapsulated EMT, with vertical risers or stand offs….like rebar.  Maybe 6-9” deep….and then backfilled…it might have been for a very high voltage run to a step down transformer.  We had 4,500 VAC incoming for some reason on a feeder to the switchgear room….been a while.

6” for EMT….mainly protection.  24” for UF.  I would still use PVC around the tree for an added level of root protection…..just not the whole run.  With a large radius arc, you can bend it and the dirt, properly compacted….in 6” lifts or layers should do just fine.

See the article for the rest.  We Engineers tend to be overly protective and err on the overkill side…

https://www.protoolreviews.com/how-to-install-underground-electrical-wiring/

Thanks for the comment.

[Specialk]

There are two considerations to account for.  The first is the 100 amp circuit protection that voltage originates from, and the next is the secondary power at the RV load panel.   The underground wire per NEC code should be rated to handle the 100 amp circuit that you mention is the origination of power. This insures that the wire does not become the weak link if there should become a fault between the RV panel and the circuit breaker/ disconnect.  The other consideration is the distance of 100 feet. Yes the RV panel is essentially providing two independent 120 volt circuits of 50 amps per leg( or 240 volt if measured phase to phase) and the 4 wire configuration ( line1, line2, neutral, ground) is necessary for the RV configuration.  The other issue is Voltage drop to not exceed 3%.  If it does at the distance you mention,  you may have some lower voltage when you push the amps higher when using.  Keeping this drop/resistance down, keeps the wire cooler, and one reason why direct burial is rated higher even though it is aluminum as the earth will dissipate heat, whereas conduit essentially insulates it.   However you will have to use conduit for your risers above earth at both ends.   
The #4 copper is also rated as such, but I think you will find that the aluminum will be less in price especially for a 4 wire run.  You will also need to run the copper in conduit as it’s not rated for direct burial. Which also will increase price.  If you are concerned with earth cover as an issue, so that you don’t come in contact with it, then bury the direct cable deeper 3-4 ft.  You have to dig a ditch regardless, going deeper would still be less cost than copper and conduit.

That’s my two cents worth.

Regards

[Bjohnsonmn]

I've just gone through a similar process with my shop.

The Coop ran Underground Service Wire (this is a specific bundle with specific insulation) from the transformer (your meter/service point in your case) to a panel (your RV pedestal in your case). My service is 200AMP, but there is a UG Service wire for 100AMP 240v with the wire gauges you need. The coop direct buried the wire with a vibrating plow with the exception of the length under the road (direction bore conduit).

How does this apply to you:

There is a specific direct bury UG service wire that will work for your use case. Menards sells it (I like that Eaton box as well as the RV supply one) I would ask a local electrician what your local code is as well as what gauge wire to use. Each county or state (in our case) has their own rules for bury depth. I would suggest going at or below the minimum. Running red plastic marking tape (cheap on amazon) about a foot down as you refill the trench gives you or someone else a visual indicator that they are approaching a wire.

[jacwjames]

Coulda Woulda Shoulda

I ran about the same length run for my garage and used a #6 awg direct bury cable.  Buried it +24" and also ran a caution tape above it after the trench was mostly filled in.  

I don't currently see a significant voltage drop but luckily power supply from the Coop is usually +120 volt only dipping to 118-119 during peak usage.   When we first moved into the house I was noticing lower voltage, my Progressive Surge protector there faults several times on this so I started to check/watch.  Voltage would have had to dip below 108 volts for the Progressive to trip.  I contacted the Coop via email and about a week later a service technician contacted me and thanked me for bringing to their attention.  They checked and had a problem with the substation feeding out area, had to turn the taps up a little on one of the transformers.  Haven't had a problem since. 

I do have a work shop in the garage mostly for wood working tools.  Also just installed a Minisplit in the work shop.   Also have an RV panel outside of the garage for visitors.  So with all that I have to watch what I'm doing as far as amp draw and but have never had a problem.  Push comes to shove I could always have any visitors hook up to a 50 amp outlet I installed on the outside of the attached garage. 

So that being said I wish I would have run a larger cable, cost wise it would have been more $$$ but I wouldn't have to worry about overload. 

I bought a 50/30/20 amp RV type panel from Home Depot, it was similar to several of the ones you listed.  But I noticed that the Siemens TL137US panel has room for 125 amp and has extra slots for more breakers so if you ever think you are going do anything else in the future that might be better off installing that for future use.

I assume you are not going to get permits or worry about an inspection.  But I would follow all codes just in case you have an unannounced visitor.   Take pictures of the trench and cable before you cover it up, use something to show depth.  An inspector might accept this but in worse case scenario make you run a new cable. 

When I was building our house and doing all the electrical after a short while the inspector concluded that I wasn't taking any short cuts and  I was following code.  When I was completing different portions of the wiring I'd call for an inspection.  If he was tied up and couldn't come he just told me to take a picture of it and send it to him and he'd acknowledge it was done.  For grounding I had to ground to the rebar in the footing, he would not accept a ground rod.  We were ready to pour the footing but he couldn't come for an inspection, I took a picture and I gave me the go ahead to pour. 

Edited August 18, 2022 by jacwjames

[Frank McElroy]

On 8/17/2022 at 7:28 PM, cbr046 said:

Gauge is easy . . . .

 

It's all the letters that dictate the right type.  Gives me something to research.  Thanks, Tom. 

If the breaker has the ability to supply 100A then I'll need to spec a cable to match.  Excellent chance we'll never see the full current unless we have 2 RV's connected, but you never know.  I'm leaning more toward #0. 

- bob

 

The chart you posted is for DC not AC. 

When running AC, you want single conductor THHN/THWN-2 wire.  For your distance 4 gauge is plenty big enough and the voltage drop will be well below 3% at 50 amps.  I used 3 4 gauge copper cables.  All the cable was black.  At both ends of one cable I put red red tape to identify one leg of the 120 volt line.  At both ends of another cable I put white tape to identify the neutral line.  I also ran an 8 gauge green cable for ground.  I then pulled all the cable through PVC conduit buried 24" inderground.

Be sure NOT to bond the ground to the neutral in your sub panel box.

There are plenty of cable calculators and charts out there but be sure you are using the proper chart for AC, not DC.

[cbr046]

49 minutes ago, Frank McElroy said:

The chart you posted is for DC not AC . . . .

There are plenty of cable calculators and charts out there but be sure you are using the proper chart for AC, not DC.

My bad, here's a chart based on feeder cable.  Quite the difference for AC vs DC -

https://inspectapedia.com/electric/Long-Run-SEC-Cable-Sizes.php

 

The question is . . . . from a physics perspective, what makes the difference?  Skin effect?  Multiple strands?

- bob