Are there limits to purchasing challenge accounts?

On iTrader, there is a limit to the total account value a single user can hold. The total balance of active Live accounts must not exceed $600,000.
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A user can have multiple Live accounts, but the combined value of all active Live accounts must not exceed $600,000 at any given time.
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If your total active Live account balance is below $600,000, you are free to purchase any number of evaluation accounts.