Easy Brain Teaser

[wirenut1980]

Without the drill running and only having the light on the circuit wouldn't the whole 240V been dropped across the lights since going around a series circuit all voltages must sum to zero? Therefore putting another (higher) resistance on this series circuit would cause less of a voltage drop across the lighting resistance. Isn't the voltage on the lights then whatever voltage is dropped across the lighting resistance? I would think less voltage drop would mean less voltage read across lighting resistance? I'm having a hard time seeing this.

It is not a matter of a multiwire branch circuit being a series circuit in this case, but rather the voltage drop on the neutral being less, or if severe enough load, could even reverse the polarity of the voltage drop of the neutral resistance, which can result in increased voltage seen at the bulb mostly. Really difficult to explain over the internet and to visualize, but easier to see if drawn out.

 

[480sparky]

Something like this?

 

[wirenut1980]

Pretty junky drawing, but makes sense to me.

This is my first time posting an attachment so hopefully it works.

 

[480sparky]

Pretty junky drawing, but makes sense to me.

This is my first time posting an attachment so hopefully it works.

I can't open it...Is it just me?

 

[billsnuff]

its a microsoft word doc. worked for me.

 

[LarryFine]

Whether a MWBC or not, this must be caused by impedance in the neutral, but it could be anywhere between the utility transformer and the panel in any case.

 

[mull982]

Pretty junky drawing, but makes sense to me.

This is my first time posting an attachment so hopefully it works.

Wirenut

Great picture helps make it easier to see. I understand it all but the last sentence.

"From circuit 1 perspective and from the light bulb?s perspective, KVL around loop 1 results in an increase in voltage dropped across the bulb and also across R_L1"

Its been a while since I've done KVL's so could you explain this last sentence.

 

[wirenut1980]

Kirchoff's voltage law in loop 1:

V_1 = (I_1*R_L1) + (I_1*Loads on L_1) + R_N*(I_1 - I_2)

If I_2 >> I_1, like during the startup of the drill motor, then it will \be additive with V_1 so to speak. Hope this helps.

 

[mivey]

What about if the lamp had a "touch" dimmer and the drill caused the dimmer to step up a notch? I have a touch lamp that steps mysteriously on a regular basis.

 

[480sparky]

.... I have a touch lamp that steps mysteriously on a regular basis.