http://forums.mikeholt.com/ en Wed, 22 May 2013 12:19:57 GMT vBulletin 60 http://forums.mikeholt.com/images/misc/rss.png http://forums.mikeholt.com/ http://forums.mikeholt.com/showthread.php?t=153687&goto=newpost Tue, 21 May 2013 23:46:12 GMT A customer contacted me and asked me to look at a project for him. He wants to build three total units, each will have a dwelling unit and two... A customer contacted me and asked me to look at a project for him. He wants to build three total units, each will have a dwelling unit and two hotel-like rooms for a total of (3) dwelling units and (6) hotel-like rooms. He requested one service to feed all the units. I did load calculations for a dwelling unit and for (2) hotel-like rooms in the first unit. My thought was to apply Table 220.84 to the (3) dwelling units since all will be supplied by the same service but I'm not sure how the hotel-like rooms should be handled. ]]> Electrical Calculations / Engineering fkimmel65 http://forums.mikeholt.com/showthread.php?t=153687 http://forums.mikeholt.com/showthread.php?t=153684&goto=newpost Tue, 21 May 2013 21:30:47 GMT Hi, in the electrical installation code of my country says something like this: if a neutral point is missing or can not be found, one of the phases... Hi, in the electrical installation code of my country says something like this:
if a neutral point is missing or can not be found, one of the phases are grounded and used as a neutral line. (not mot a mot but roughly so)
so what do you think ? is it possible or just a mistranslation from german standards? ]]> Electrical Calculations / Engineering electrics http://forums.mikeholt.com/showthread.php?t=153684 http://forums.mikeholt.com/showthread.php?t=153680&goto=newpost Tue, 21 May 2013 18:37:19 GMT When installing a 1200 amp 3 phase Transfer Switch, between incoming service and the main service disconnect (1200 amp 3 phase 480 volt breaker, 4... When installing a 1200 amp 3 phase Transfer Switch, between incoming service and the main service disconnect (1200 amp 3 phase 480 volt breaker, 4 wire system). Contractor is proposing 4 parallel runs of 350 mcm or 3 parallel runs of 600 mcm 90 degree conductors THHN and 90 degree terminals. My calculations are 1120 and 1140 amps respectively considering de-rating for the 4th current carrying conductor (the neutral). Would either of these be sufficient to supply the 1200 amp main switch, using the next size overcurrent device as exampled in section Article 240.4 (C) ? ]]> Electrical Calculations / Engineering maxamps http://forums.mikeholt.com/showthread.php?t=153680 http://forums.mikeholt.com/showthread.php?t=153666&goto=newpost Tue, 21 May 2013 07:05:19 GMT We have around 50 distribution panels (120/240V) spread on 5floors. We need to monitor loss of voltage at individual panels. We are not going to... We have around 50 distribution panels (120/240V) spread on 5floors. We need to monitor loss of voltage at individual panels. We are not going to monitor each feeder breakers from each of the panels, but just the main breakers at the DP. The control room is in a different building. What is the best way to monitor loss of voltage at each of these panels such that the operator comes to know something is wrong at a particular room. Using a relay is not an option..
Thanks in advance for the help! ]]> Electrical Calculations / Engineering ucdoshi http://forums.mikeholt.com/showthread.php?t=153666 http://forums.mikeholt.com/showthread.php?t=153660&goto=newpost Tue, 21 May 2013 00:25:15 GMT I keep coming across this and need some more people to weigh in. Say you are loading up a 120/240V panelboard, balancing the loads in amperes. So on... I keep coming across this and need some more people to weigh in. Say you are loading up a 120/240V panelboard, balancing the loads in amperes. So on the sides of my panel schedule, I have so many amps running on each line for each load, which of course are calculated based on whether the load is 3-phase, single phase, or 120V single phase. Do I sum total all of the 'A' line currents, 'B' line currents, and 'C' line currents and that is what the panelboard size should be based on? Is that the actual current running on the lines?

After I have the loads balanced as best I can, if I take the total KVA on the panelboard and divide by 240 3-phase, does that number hold any relevance? (This is how I'd typically size a 120/208 or 277/480...) It ends up being less than the calculated individual line currents, so I don't want to undersize any feeders! I'm just not sure if this is the real number that the service sees and the line currents calculated above are only used to balance the panelboard.

Thanks! ]]> Electrical Calculations / Engineering apelk http://forums.mikeholt.com/showthread.php?t=153660 http://forums.mikeholt.com/showthread.php?t=153658&goto=newpost Mon, 20 May 2013 23:08:04 GMT Hi all, I have a question regarding the Full load current in Active Front end drive(AFE) that is used to drive a propulsion Motor. I learn from... Hi all,

I have a question regarding the Full load current in Active Front end drive(AFE) that is used to drive a propulsion Motor.

I learn from my previous projects that the full load current for the AFE is less than the full load current that is sent to the motor from the AFE.
Eg: IF the motor full load current is 2900 Amp then the full load current for th AFE that is used to drive this motor is only around 1600 amp. Why is there a difference ?

Also, do AFE's account for Short Circuit Current ?
Thanks ]]> Electrical Calculations / Engineering ElecEng http://forums.mikeholt.com/showthread.php?t=153658 http://forums.mikeholt.com/showthread.php?t=153656&goto=newpost Mon, 20 May 2013 21:18:58 GMT Have an existing 1phase parallel 1/0 Service(300A). I am assuming a 300A Services per 310.16(2008). If I wanted to change from the parallel... Have an existing 1phase parallel 1/0 Service(300A). I am assuming a 300A Services per 310.16(2008). If I wanted to change from the parallel conductors on load side of meter to 250kcmil per Table 310.15(B)(6), wouldnt i still be code compliant. Just feel like it would be easier to terminate in a Main Service breaker enclosure an then into a transfer switch. ]]> Electrical Calculations / Engineering wmeek http://forums.mikeholt.com/showthread.php?t=153656 http://forums.mikeholt.com/showthread.php?t=153655&goto=newpost Mon, 20 May 2013 19:40:21 GMT I currently have a meter base and service equipment located at a pole barn on a piece of property.Property owner wants to build a home approx. 150' from the existing structure and supply it with it's own metered service. He contacted the utility and was told that as long as the existing service is sufficient in size he will have to go with one meter for the address..Would the conductors from the existing to the new home be considered Service Entrance Conductors? At that point coming from the meter to the house (120/240V single phase) can it be 3 wire or does it need to be 4. Thanks. ]]> Electrical Calculations / Engineering nizak http://forums.mikeholt.com/showthread.php?t=153655 http://forums.mikeholt.com/showthread.php?t=153654&goto=newpost Mon, 20 May 2013 19:39:32 GMT On another forum an electrical contractor that has gotten an engineering degree was wondering if he could use his EC seal (A NJ thing) to seal... On another forum an electrical contractor that has gotten an engineering degree was wondering if he could use his EC seal (A NJ thing) to seal prints.

Some of us pointed out that he was not an engineer until he took and passed a test while others feel he is an engineer because he has an engineering degree.

It was also stated that he could do electrical engineering and just have PE stamp the work. I feel that is also false.

So what is the straight dope on this?

TIA, Bob ]]> Electrical Calculations / Engineering iwire http://forums.mikeholt.com/showthread.php?t=153654 http://forums.mikeholt.com/showthread.php?t=153650&goto=newpost Mon, 20 May 2013 17:08:42 GMT Conducting an Arc Flash Study for a client that of which I'm nearly complete with. Everything looks pretty good except for one anomaly and I need a sanity check. At one point in the system I have a 480VAC, 250A, MLO, 3-Phase I-Line Panel with a Category 0 Incident Energy and Isc value of 8.76kA at this bus – I have no problem with this. This panel has a 125A breaker that feeds 75kVA Transformer (480-120/208, Delta-Wye) to a 225Amp Distribution Panel (typical step down). This distribution panel has a 225A MCB (120/208, 3-phase, 4wire) and is a Square D, QO Panel. At this point in the system, my calculated Short Circuit (Isc) is 2.67kA which I feel is fine due to cable and transformer impedance knocking this down. My concern is the Incident Energy Level is a Category 4. Now I understand that the Incident Energy calculated is a combination of the Short Circuit Current available and the Protection Device Clearing Time and based on the TCC curve of the Main Breaker on the QO Panel, this makes sense. Even if you use the OCPD upstream (the 125A in the I-Line) you still have a Category 4. I guess my question or sanity check is this – could having too low of a Short Circuit Rating (2.67kA) actually be creating a higher Arc Flash level due to a long clearing time? It just seems odd that you can have a Category 0 Level on a higher voltage and amperage rated panel and need much more PPE for a run of the mill QO house panel. Am I crazy?

Some background – using ETAP Version 12.0.0, Assuming 3-phase, Sym ½ Cycle fault. Below is a link on the curve of the MCB on the QO Panel, Page 18 of 20:

http://www.global-download.schneider...%20-%20734.pdf ]]> Electrical Calculations / Engineering PSU Electrical http://forums.mikeholt.com/showthread.php?t=153650 http://forums.mikeholt.com/showthread.php?t=153646&goto=newpost Mon, 20 May 2013 15:08:37 GMT For a quick way to calculate a minimum neutral size, could you base that calculation on the ungrounded conductors or breaker? e.g. 3ph 4 wire... For a quick way to calculate a minimum neutral size, could you base that calculation on the ungrounded conductors or breaker?

e.g. 3ph 4 wire service/feeder 600A breaker. The first 200A at 100% and then the balance of 400A at 70% = 200 + (.70 * 400) = 200 + 280 = 480A

e.g. 3ph 4 wire service/feeder (2) 500MCM AL XHHW rated 620A. The first 200A at 100% and then the balance of 420A at 70% = 200 + (.70 * 420) = 200 + 294 = 494A = (2) 350MCM

This idea just popped into my head as I read Article 220 and I'm blurting it out. ]]> Electrical Calculations / Engineering conmgt http://forums.mikeholt.com/showthread.php?t=153646 http://forums.mikeholt.com/showthread.php?t=153645&goto=newpost Mon, 20 May 2013 14:41:26 GMT Hopefully I am not asking a question already posted. I have seen some questions related to residential service sizes, but nothing to answer my... Hopefully I am not asking a question already posted. I have seen some questions related to residential service sizes, but nothing to answer my questions. We are involved in a project that is installing 1 hp, 240v, 1ph sewer grinder pumps in residential neighbor hood. Each home owner is getting one. We instructed the electrician to provide a service calculation for each resident to determine if a service upgrade is needed. The calculation was based on Example D2(b) of the 2005 NEC. First question - if the calculation totals 85 amps (including new load) will the existing 100 amp service be adaquate per code? Where would an upgrade be required, over 100 amps? I would contend the countertop mounted microwave is not a fixed appliance and would be included in the small appliance load - yes/no? I have seen from some other posts that it is possible to have more than 2 small appliance circuits. Has anyone seen 4, 5 or 6 small aplliance circuits? Some of the residental calculations have that many. If a circuit is dedicated to the countertop is that what will label it as a SAC? Any insight would be appreciated. ]]> Electrical Calculations / Engineering thepij http://forums.mikeholt.com/showthread.php?t=153645 http://forums.mikeholt.com/showthread.php?t=153625&goto=newpost Sun, 19 May 2013 21:30:49 GMT I have a site with a couple small open pavilions on it, then one main pavilion with a eating area and kitchen, and then a equipment room. The... I have a site with a couple small open pavilions on it, then one main pavilion with a eating area and kitchen, and then a equipment room. The equipment room and main pavilion will have their own services but in the open pavilions they want a few receptacles and a light in each open pavilion. I was thinking of mounting a little 30A rated panel on each pavilion that could hold maybe (2) 20A circuits each. Each pavilion would need a little panel because each one is its own structure right? I Wouldnt be able to feed the lights/receptacles direcrly correct?

Also, would the little panels have to be rated for 100A each, as required by some section in the NEC that I would need my code book for. I think it is article 230 but thats probably for residential only.

Thanks guys. ]]> Electrical Calculations / Engineering Npstewart http://forums.mikeholt.com/showthread.php?t=153625 http://forums.mikeholt.com/showthread.php?t=153623&goto=newpost Sun, 19 May 2013 19:50:29 GMT I am a bit confused with this; Service is 277/480V 3 phase. The question says; what is the ampacity of a cable supplying a lighting load... I am a bit confused with this;

Service is 277/480V 3 phase.
The question says; what is the ampacity of a cable supplying a lighting load (Lighting is supplied by 277V).
Lighting Panel "LP" is a 3 phase panel.
Total Lighting load is 65000VA

Do I start with this;
I = 65000
480x1.73

OR is it
I = 65000
277x1.73

of cause I will then use the 125% ]]> Electrical Calculations / Engineering schicco http://forums.mikeholt.com/showthread.php?t=153623 http://forums.mikeholt.com/showthread.php?t=153596&goto=newpost Fri, 17 May 2013 20:24:39 GMT What is the difference between SPD & SSD? (Surge Protection Device & Surge Supression Device) Where it is located? Meter or SE vs branch circuit protection? ]]> Electrical Calculations / Engineering ptonsparky http://forums.mikeholt.com/showthread.php?t=153596