Power to a boathouse

Reply

  #1  
Old 05-07-14, 07:43 AM
Member
Thread Starter
Join Date: May 2014
Location: United States
Posts: 8
Power to a boathouse

I have a boathouse which the builder installed a 50A panel and wired some outlets and three lights. If I recall there are two 20A circuits installed. That construction passed inspection. Now I need to run power to that panel. The boathouse is all wood construction; wooden piers/pilings into the lake bed.

I have two boat lifts 12A each that plug into already wired outlets. Other than the lights, I plan to install a ceiling fan (no light kit) and a mini fridge. There will be some plug-in incidentals like radio, battery charger, etc. Everything is 120V. I have absolutely no need for 240V. if I ever did need 240v on the boat dock I have a portable generator I could use. Also it is exceedingly rare that both boat lifts would be operating simultaneously.

From the main panel in the house to the panel in the boathouse shed itís 160-ish feetóthe path I plan to run the wire. I have 181 feet of UF direct bury 8-2, underground PVC, 30a breaker for the main panel, 6ga bare copper and a grounding rod.

My plan was to supply 120V (why I got 8-2 because itís cheaper) in the conduit. Ground the boathouse panel with the 6ga bare copper & grounding rod back on shore.

Reading various threads on here, code says I need to pull 4 wires to the boathouse panel regardless. Is that really the case for my situation? Do I need to put the UF 8-2 on craigslist and go get x-3 instead? Seems over the top to me to put 240 where it isnít necessary.

Thanks!
ML
 
Sponsored Links
  #2  
Old 05-07-14, 08:17 AM
pcboss's Avatar
Forum Topic Moderator
Join Date: Jul 2002
Location: Maryland
Posts: 14,356
Running two hots will give you the ability to have twice the power available.

Running UF in conduit will be a pain. Use individual conductors.
 
  #3  
Old 05-07-14, 08:40 AM
Member
Join Date: Oct 2013
Location: United States
Posts: 235
Boat House

When you mention 240V, you are really running two 120V legs to the panel so as mentioned twice the power. You don't really operate anything on 240V by itself.
At 120V with 30amps at 160ft your volt drop will be around 6.5% when one of the boat lifts is operating. Without any lifts operating and figuring 18 amps your VD Drop would be around 3.75%. If you run the 2-hots, Neutral and ground #8 your VD with one lift running would be around 3.13% and with no lift, just under 2%. It may not seem logical now but installing 120/240 is what you should do.
 
  #4  
Old 05-07-14, 10:00 AM
Member
Thread Starter
Join Date: May 2014
Location: United States
Posts: 8
Yep. I am aware 240v is essentially 2 120v (see aside below).

I'm not really pulling the wire through the conduit as much as sliding the conduit over in 10' sections. I know this will take longer, but my time is free to me.

So what do you think is the most cost effective way to get me out of the X-2 pickle? Go get a single strand and add that as another hot lead in the conduit?

Thanks!
ML

Aside: This is why electricity just does not make sense sometimes. I understand the voltage drop, and I trust your calculations. But if the way to get to 240 is by 2 120, then why is the voltage drop less? You would expect it be twice. . .the voltage drop for each hot conductor! grrrr. End Rant.
 
  #5  
Old 05-07-14, 10:18 AM
ray2047's Avatar
Group Moderator
Join Date: Mar 2006
Location: USA
Posts: 32,644
<Aside>
240v is essentially 2 120v
No. Your house is suplied with 240 volts not two 120 volt legs. The 120 is derived from either leg of the 240 by using one leg of the 240 and the grounded center tap from the secondary of the supply transformer (AKA neutral). By running two 240 legs you double the number of sources for 240 to use with a neutral to derive 120 volts.

Name:  TransformerB.png
Views: 775
Size:  20.6 KB

Now the more technical aspect. You only need one neutral because some of the return current goes back on the 240 leg. The neutral only caries the difference between the amps on 240 leg A and 240 leg B. Example 30 amps on A and 20 amps on B neutral only carries 10 amps (30-20=10) .Worse case all amps on one leg the amperage can still not exceed the breaker size and the neutral is sized to that (50 on A - 0 on B = 50 amps on the neutral).
 
  #6  
Old 05-07-14, 10:44 AM
Member
Thread Starter
Join Date: May 2014
Location: United States
Posts: 8
Ahhh. . .Previous misinformation received (not from here) getting flushed out.

So, to put it another way, 120v isn't supplied to my main panel. It is derived in the panel?

Therefore in my x-3 wire, the two hots each carry 240v and I derive the 120v in the 'sub panel' again.
 
  #7  
Old 05-07-14, 11:18 AM
ray2047's Avatar
Group Moderator
Join Date: Mar 2006
Location: USA
Posts: 32,644
Yes, you have it.

.
 
  #8  
Old 05-07-14, 11:49 AM
Member
Thread Starter
Join Date: May 2014
Location: United States
Posts: 8
Thank you.

"Now that begs the question. Must I run two hots to deliver 240?"

Scratch that. If I don't have the two hots I cannot derive 120v. I have a 240 circuit.
 

Last edited by ml18911; 05-07-14 at 12:07 PM.
  #9  
Old 05-07-14, 12:35 PM
ray2047's Avatar
Group Moderator
Join Date: Mar 2006
Location: USA
Posts: 32,644
Must I run two hots to deliver 240?
Yes.
If I don't have the two hots I cannot derive 120v.
You need only one hot for 120 volts.
 
  #10  
Old 05-07-14, 07:38 PM
Member
Join Date: Oct 2013
Location: United States
Posts: 235
Boat House

But if the way to get to 240 is by 2 120, then why is the voltage drop less? You would expect it be twice. . .the voltage drop for each hot conductor! grrrr. End Rant.
Your house is 120/240 Single-Phase 3-Wire as ray explained. The voltage-drop is less when you split the 120V loads using each hot with the common neutral. As an example you have two boat lifts at 12 amps each that are 120V. If you put both on the same hot leg and the(GCC) neutral the voltage drop for that would be based on 120V available and 24 amps of load. By using the 120/240 1ph3w at your boat house panel, you put one lift on one hot and the common neutral and the other lift on the other hot and the common neutral and the load on each of those 120V circuits is 12 amps each and the neutral (which carries the difference between the two hots, as ray explained) will have zero amps. The voltage drop for that 120/240 system is figured with 240Volts and the same 24amps and the percent of voltage drop is lower because the voltage is higher. The number of volts that drop is the same for 120 or 240 it is the percentage of drop that is changed by using a higher voltage and we like to keep voltage within a certain percent range so the system will operate correctly.
 
  #11  
Old 05-08-14, 05:22 AM
Member
Thread Starter
Join Date: May 2014
Location: United States
Posts: 8
OK. I believe I understand the WHY well enough now behind running two hots.

Anyone have a suggestion on the most cost effective way at this point for the HOW?

I have, in my grubby mits, 181 feet of UF 8-2. Sell this getting what I can and buy all new? Or can I buy one more THWN lead to run another hot along with my 8-2 in the conduit?

Thanks!
ML
 
  #12  
Old 05-08-14, 06:19 AM
ray2047's Avatar
Group Moderator
Join Date: Mar 2006
Location: USA
Posts: 32,644
can I buy one more THWN lead to run another hot along with my 8-2 in the conduit?
No. All conductors must be in the same raceway. In this case that would be the sheaf of the UF not the conduit. (It's to cancel out stray electromagnetic fields that can produce heat.)
 
  #13  
Old 05-08-14, 07:03 AM
Member
Thread Starter
Join Date: May 2014
Location: United States
Posts: 8
Rats.

But if I use individual conductors as pcboss suggests above, the conduit would be the raceway. So that's OK?

Anyone want to buy 180' UF 8-2?

Thanks!
ML
 
  #14  
Old 05-08-14, 08:02 AM
ray2047's Avatar
Group Moderator
Join Date: Mar 2006
Location: USA
Posts: 32,644
But if I use individual conductors as pcboss suggests above, the conduit would be the raceway
Yes.

.
 
  #15  
Old 05-20-14, 07:07 AM
Member
Thread Starter
Join Date: May 2014
Location: United States
Posts: 8
Ok, I'm back.
Thanks for all the help so far. I have pulled all the wires, and now ready to connect everything up this coming weekend.

One final question: would it be wise to install a 30A GFI breaker to supply the boathouse in the main panel?

Thanks!
ML
 
  #16  
Old 05-20-14, 07:51 AM
Tolyn Ironhand's Avatar
Group Moderator
Join Date: Nov 2007
Location: Twin Cities, MN
Posts: 11,981
I would not because if it trips you would have to walk back to the house to reset it. I would install all the GFCI's in the boat house where they would be easy to reset.
 
  #17  
Old 05-20-14, 10:42 AM
CasualJoe's Avatar
Member
Join Date: Jan 2010
Location: USA
Posts: 9,213
I have a boathouse which the builder installed a 50A panel and wired some outlets and three lights. If I recall there are two 20A circuits installed. That construction passed inspection.
You should already have GFCI protection where needed since it has already passed inspection.
 
  #18  
Old 05-20-14, 11:34 AM
Member
Thread Starter
Join Date: May 2014
Location: United States
Posts: 8
CasualJoe,

And if it does not? This forum is littered with questions/conditions where things somehow passed inspection yet are not code-compliant.

I just want to ensure that the end result is right. The very last thing I want is someone seriously injured or killed getting out of the water at my dock because something isn't right or I was unwilling to walk 100 steps to reset a tripped breaker.

And to those whose opinion is I should hire a professional to do it. That may have gotten me out of some work. But in this case my concern would remain that the job be done right.

If memory serves the already installed breakers are not GFI in the boat dock panel. I could be wrong, but that's what I remember. I'll check this weekend.

Any issues if I install GFI in the main panel and GFI in the boat dock panel (other than extra cost)?

Thanks!
ML
 
  #19  
Old 05-20-14, 05:31 PM
CasualJoe's Avatar
Member
Join Date: Jan 2010
Location: USA
Posts: 9,213
Any issues if I install GFI in the main panel and GFI in the boat dock panel (other than extra cost)?
Yep, you'll probably have nuisance tripping. You never want GFCI protection at more than one point in the circuit.

And if it does not? This forum is littered with questions/conditions where things somehow passed inspection yet are not code-compliant.
If the existing installation has no GFCI protection it would not be code compliant and shouldn't have passed inspection nor should you have paid the builder. Call the builder back if there is no GFCI protection, you paid for it. Sadly, there are a lot of inspectors out there who aren't code saavy.

If memory serves the already installed breakers are not GFI in the boat dock panel. I could be wrong, but that's what I remember. I'll check this weekend.
The most commonly used form of GFCI protection is not with GFI breakers, but is by installing a GFCI receptacle at the first receptacle which has the capability to protect all downstream receptacles. Check to see if that's what you have.
 
Reply

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
Display Modes
'