ADE7880 reporting big voltage drop with motors

Question

My mains supply here is 230Vrms and the ADE7880 is reporting this correctly. 
 When I switch on am appliance with a motor such as a hairdryer or vacuum cleaner the Vrms reported by the ADE7880 drops down to around 150-180V however a multimeter will still measure the mains are 220-230 Vrms. 
 Is this to be expected? Any idea what could be causing the ADE7880 to report such a low Vrms compared to a multimeter. 
 Here are some waveforms exported from the ADE7880. Apologies but I'm not using the high speed data port so the sampling rate is a bit low. 
 With mainly resistive loads - peak instantaneous voltage around 310V. 
 
 With hairdryer on - peak instantaneous voltage now around 220V with what looks like some form of clipping? 
 
 Vacuum cleaner - similar to hairdryer.

dave.smith · Accepted Answer

It appears you have a current dependent voltage drop. Either the voltage channel measurement is in the wrong spot. Should be before the load and the first measurement from the wall power or your wire gauge is to small. 
 
 Try measuring the voltage drop from the wall connection to the point where the resistor divider is connected to the line with a volt meter. you should not have a voltage drop. 
 
 measure green should be wall power 
 measure red with and without load

Dave

Electronic Design Services - PartnerZone

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ADE7880 reporting big voltage drop with motors

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