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Activities with negative float

6 replies [Last post]
Wed, 2009-09-30 07:28
Jhorbam Baena Orozco
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Hi...my problem is the follow...i have a group of activities that show a negative float but by the times the float must be positive...by example:

Project Start 04OCT2009, Project Finish 21OCT2009
Activity 1 ES=04OCT2009, EF=06OCT2009, Float= -24.

I think that the problem is in the relationship but all the activities have FS relation whit no lags...have the same calendar, have assigned resources and why that negative float is showing but Primavera?..

THANKS FOR ALL THE HELP.
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Replies

Wed, 2009-09-30 08:42
#1
Rafael Davila
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Jhorbam

Usually constraints either on global job duration or on individual activities are the origin of negative float. If you already ruled out this possibility the next thing I can think of is out-of-sequence updating.

Your schedule report in P3 will provide you with a listing of out-of-sequence occurrences; some are due to errors in data entry. If your report do not shows out-of-sequence occurrences I would go back to double check on constraints, also shown in this report.

The other thing I can think of that might generate negative float is resource leveling, because P3 software do not show true critical path under resource constraining this is more difficult to detect. Again in your schedule report the settings for resource leveling will be exposed.

I avoid the use of multiple calendars but this might also be another reason for aparent inconsistencies in the float calculation.

Best regards,
Rafael
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Wed, 2009-09-30 08:15
#2
Jhorbam Baena Orozco
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Yes Rafael...I have a Constraint Must Finish...but the date of that activitie is 21OCT2009...so how that can affect in the negative float?...can you explain me?...THANKS
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Wed, 2009-09-30 08:06
#3
Rafael Davila
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Check if there is a Must Finish By constraint in the project overview.
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Wed, 2009-09-30 07:46
#4
Gary Whitehead
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Some other things to check are:

Are there any constraints on the activites showing negative float?
Any target dates?
What calendar is assigned to these activities?
What activity types are they (eg ASAP, hammock, etc)?
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Wed, 2009-09-30 07:36
#5
Jhorbam Baena Orozco
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Jared Thanks, but the last activity finish the 12OCT2009...What could be happen there?
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Wed, 2009-09-30 07:33
#6
Jared Williams
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Float is calculated on the backwards pass, and is based on the successor ties of the activities. It is also the net of the entire group of activities, not just the one. So if you activity 1 has a successor activity 2 that goes 24 days later than the 21OCT09 date all the activities in that path are given a -24 float.

hope that helps, also check for activity constraints
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