computer problems

[Smart $]

ever heard of harmonics?? shared neutrals feeding computer equipment causes harmonic currents returning to the panel that do not cancel each other out like on normal loads. it's because the returning current is returning at a different frequency due to the switching in the computerized equipment's power supply. these harmonics are going to cause fluctuations in system voltages. every computer's instructions begin with the suggestion of installing it on a dedicated circuit.... if this common neutral was oversized enough the effects of harmonics would be lessened.

An oversized neutral on the MWBC's is also suggested and IMO preferable to dedicated circuits.

However, oversizing and/or dedicated neutral conductors do not alleviate harmonics on a system. With the exception of a minor change in voltage drop, all that changes under these different wiring methods is where the harmonics add up.

As I have learned here, the best [simple] solution is to put computer circuits on a single phase, three wire system. While there will still be switching distortion, at least it won't add up as on a three phase system.

 

[iwire]

ever heard of harmonics??

Of course, and they while PCs are often a cause of harmonic currents I do not believe they effect the PCs operation.

shared neutrals feeding computer equipment causes harmonic currents returning to the panel that do not cancel each other out like on normal loads.

It's not the shared neutral that 'causes the harmonic currents' it is the PCs power supply that causes the harmonic currents.

Run a two wire branch circuits to each PC and you will still get additive harmonic currents on the feeder neutral

every computer's instructions begin with the suggestion of installing it on a dedicated circuit....

A MWBC can still be a 'dedicated' circuit.

If it's left to me I would not use MWBCs in a data room as they would not be that advantageous, but we always use them in office buildings, offten the modular furniture comes set up for MWBCs.

 

[JdoubleU]

voltage fluctuation

voltage fluctuation

ever heard of harmonics?? shared neutrals feeding computer equipment causes harmonic currents returning to the panel that do not cancel each other out like on normal loads. it's because the returning current is returning at a different frequency due to the switching in the computerized equipment's power supply. these harmonics are going to cause fluctuations in system voltages. every computer's instructions begin with the suggestion of installing it on a dedicated circuit.... if this common neutral was oversized enough the effects of harmonics would be lessened.

A voltage fluctuation is normal isn't it, as long as it doesn't exceed 5%. Shouldn't computer be able to operate normally within that voltage fluctuation.

 

[charlie tuna]

in the early ninties harmonics was a growing problem and computerized equipment of all types began to build filters in their power supplies to minimize harmonic currents in the return neutral. and it was expected that harmonic problems would increase and then disappear ??? i have witnessed many problems with computerized equipment on shared neutrals with other loads. our recommendation at that time was to install the effected equipment on dedicated circuits and seemed to always solve the problem. and we have done enough power quality studies to see voltage variations to sensitive equipment caused by loads on other circuits within a multi wired branch circuit.

 

[dereckbc]

A voltage fluctuation is normal isn't it, as long as it doesn't exceed 5%. Shouldn't computer be able to operate normally within that voltage fluctuation.

Yes, today’s switch mode power supplies can operate quite well from 90 to 180 VAC input and beyond in quality made SMPS. So 5% is meaningless to SWPS. The SMPS in my PC I built works from 70 to 300. VAC input

Furthermore SMPS are not affected by harmonics, they only generate them. Any SMPS converts the AC line directly to DC via a bridge diode circuit which doesn't care if it is clean 60 Hz or some third harmonic variant, it still comes outs as DC on the output of the rectifier.

 

[robbietan]

Yes, today?s switch mode power supplies can operate quite well from 90 to 180 VAC input and beyond in quality made SMPS. So 5% is meaningless to SWPS. The SMPS in my PC I built works from 70 to 300. VAC input

Furthermore SMPS are not affected by harmonics, they only generate them. Any SMPS converts the AC line directly to DC via a bridge diode circuit which doesn't care if it is clean 60 Hz or some third harmonic variant, it still comes outs as DC on the output of the rectifier.

I may have to disagree with the statement sir, only if just a little bit.
SMPS needs a certain 'peak value' of the waveform in order to conduct. if the waveform is flat topped, there may be problems with the SMPS. However, this does not seem to be the problem, as it would take a multitude of desktop PCs to flat-top the AC waveform

 

[dereckbc]

I may have to disagree with the statement sir, only if just a little bit.
SMPS needs a certain 'peak value' of the waveform in order to conduct. if the waveform is flat topped, there may be problems with the SMPS.

Flat-topping from a commcercial hard source? I do not think that is even possible, well maybe if there is PWM motor controls, I may be wrong but I just don't see it. Besides even if it is possible, any PC SMPS shouldn't be affected as they will work for a $100 UPS that generates a 60-Hz sqaure wave which is flat as you can get.